I'll go through them all, starting from the real beginning of the Heisei era- 1989!
BLACK RX: RX vs. Naya Goro. What's not to love? Shame they couldn't work the other 10 Riders in more though. The best multi-Rider finales strike a balance between giving them time to shine while also remembering who the main man is (see: Stronger, New Kamen Rider.)
Shin: Gore galore. "Level 2" is not the most threatening name in the world, but he puts up a good fight. And how cool was that escape?
ZO: The whole "absorbing" thing is kinda weird, but that's Doras for you. Has the best music ever when Red Doras appears- It's both sinister and funky!
J: Of course the giant part's great, but I suppose the true End Fight is J vs. a muppet. Hey, it surprised me the first time.
Kuuga: Eerie, brutal and unconventional, just like the rest of the show! Truth be told, looking back on it now, it feels more bizarre and dreamlike than an epic final battle, but that's the idea. For a show that's loaded with violence, I always felt Kuuga always had a anti-violence streak bubbling just underneath the surface. Never more is this clear than during the final battle, with Godai reduced to tears. He overcomes the darkness of Ultimate Form and beats Daguba, but the tone isn't overtly triumphant. It's not so much going out with a bang as with a wet, bloody thwack followed by that cathartic finale.
I like how Daguba, despite being the ultimate evil (until the next series) has his weakness in his belt buckle. Rider monsters have been wearing belt buckles since the beginning. Hell, it kinda feels wrong to me when they don't. It's the status identifier, the thing that keeps everyone on the same team no matter how different they look. You never think of it being much more than that, but Kuuga took it up a level.
It's important. We're never told exactly why, but we get hints. Rose lady doing that "unlocking" thing. They're prominently shown when some monsters explode. The different colors for the different tribes. The Salamander guy (we never saw his monster form, but it was a salamander) polishing up Daguba's buckle. There's a lot of build-up so it becomes almost screamingly obvious. That it's a counterpoint to Kuuga's buckle makes it even better. Sure Daguba is still going after its broken, but he might as well be a dead man walking from that point.
Although I guess the true final battle of the series would be Godai trying to get past airport security in Cuba.
Agito: I've always loved this one, but likely not for the same reason as most. Agito kicking what's essentially "God"/Satan/Evil Incarnate/The Power Cosmic/Darkness/Whatever is exciting, but it's the fight beforehand that I love. It is small-scale, basically just a bunch of guys yelling and hitting each other. It looks like it's filmed in my backyard. But therein lies the real coolness.
Some of modern Kamen Rider's best moments are when it simply evokes the old series, not through blatant parallels or hit-you-over-the-head referencing, but just doing something in the way the older series might. I'll get back to this with Decade, but Agito does it too. In the end it's a couple of guys fighting for the fate of the world in the woods. It's a small little event with potentially huge ramifications.
When I watched this with my dad in 2002, he thought that the show was going to build up to this big Agito-Unknown War with armies on both sides. A "whole-of-humanity-rises-up" sort of thing. I can see how you might think it's going there what with seemingly every other person starting to turn into an Agito by the end. But I like that no, it's ultimately all about 3 Riders, just like they promised at the start of the series. Shôichi is an Agito, but he's also Kamen Rider Agito.
Ryuki: I guess the final battle is Knight vs. Odin? Or would it be Ryuki's final battle against a bunch of movie leftovers? Either way it doesn't matter since it didn't happen! Except when it did, to make it un-happen.
Anyway, the real final battle for me is in the movie, Ryuki vs. Ryuga right up to the climax. One of the most exciting fights of the series, literally smashing every rule in the show- now they're in the real world! The Dragons come out of the ground! They transform right to Survive Mode! Shinji kills! He does, if you think about it, though I guess Ryuga's pretty much no different than any other Mirror Monster, because while he has sentience, he arguably doesn't have a conscience. Too bad we never got to find out what happened next, though in my head they win. Then have a lot of explaining to do.
Faiz: I'm of two minds on Faiz's final battle: on the one hand, what is up with all the last-minute property damage? Auto-Vajin bites it and I'm pretty sure the Kaixa belt didn't come out of that one well. Was that necessary? On the other, Teruo blows the hell up (yay!) and it's a pretty exciting battle.
I'm not sure what happened with Kiba... I mean I know he apparently died, but a little more resolution would have been nice considering he's practically the main character at the beginning. I'm fine with the sacrifice, especially given what he turns into during the last few episodes, but that's it? Those two idiot cops get more of a resolution! Okay, just sticking to the final battle though, I like it.
Blade: As I've said before, I like both the TV and Movie endings. As for the actual final battles, the movie one is more triumphant and focused on spectacle (King Form RSF's a giant monster!) while the TV one gets back to that thing Agito did where it's just some guys in the woods, but it's massive in scope. You really do feel like this is the most important battle ever. Everything's on the line. Roaches are closing in on his friends and Kenzaki's up against the one guy he really came to count on (and vice-versa.) The ending was a shock when I first saw it and remains so even today. It's vicious.
Hibiki: The battle that should have been the final battle just ends up being finished offscreen, and the actual final battle is... what, Hibiki vs. a Hammerhead Centipede? A letdown from Orochi, to be honest. Granted in the TV show he's built up so much that he's going to be like the worst thing ever, but c'mon- Movie Hibiki beat him after a quick trip the hospital, some Oranamin C and getting a magic sword. I would have liked to see something more "break the cycle". Hibiki ends the eternal struggle with the Makamô, but at great cost to himself or his friends.
THE FIRST: Obviously, it's a ton of fun if you consider the battle beginning the moment they jump out of the water. Classic poses! Shocker guys melting! Rider Double Kick! I always felt it was weird to put Snake & Cobra last, since they're the most sympathetic villains. It's sort of a "Well, um, jeez..." moment that kills the heroic enthusiasm. But then this is the newer, angstier revamp series!
Well actually, I guess the last villains in the movie are random scientists and an Evil Control Panel™! With that kick-ass music. Oh heck, I like it.
Kabuto: I liked it back in 2007, when I remember it taking a lot of flack because most were still holding out hope we'd get Kabuto vs. Dark Kabuto in New York, in the middle of a volcano and in spaaaaaaaaaace like Terebi-Kun "predicted". Or maybe just answers to the million-billion questions plaguing our minds. It was alright with me though. The last episode just keeps raising the stakes and the culminating final battle is... well, it's Kabuto-ish.
Looking back now I can freely admit that it's some of the most seat-of-your-pants writing to ever come out of televised Rider. Tendô is in full-on God Mode, escaping certain death, leaping off of towers and destroying meteorites with flower power. The Perfect Zecter gets wrecked, but who cares, right? Kabuto & Gatack working together was cool though. Then Dark Kabuto dies for some reason. You have to love that the show ultimately comes down to a middle-aged guy beating up Zectroopers and screaming at Kabuto. There's got to be some subtext in there somewhere. Like the finale as a whole (which I know I've yammered on about before) I love every minute of it.
Den-O: I liked it a lot. It was one of the most all-round satisfying final battles in a while, giving everybody a chance to shine and throwing nothing to lions (Uratatos suddenly dies! The Den-Liner blows up! etc.)
But then, it's not the end anymore now is it?
THE NEXT: God that was awesome! A massive rumble in a restaurant, with the Double Riders vs. Scissors-Jaguar and V3 vs. Chainsaw-Lizard, plus helpings of Shocker Riders and henchmen all around! Hurricane smashes through the window! Rider 2 is in such bad shape he's spitting blood! Hongô performs a Rider Kick unmasked! The ultimate final battle!
...sorry, I forget what happens after that. Wasn't there something about a girl or something? Guess it wasn't really important.
Kiva: So is the final battle the two Kivas vs. the Bat Fangire, or 3 Kivas, IXA, & the Arms Monsters vs. Giant Glowing CGI Vortex?
In any case, I liked the final battle(s) in this show. Admittedly I do have some problems: the way Riders get tossed aside kind of irks me. It's like TheBee in Kabuto: everybody who was TheBee goes on to become something stronger anyway, so "Kamen Rider TheBee" is just a suit in the end, not a character himself. We've got that here with Taiga dumping Saga in favor becoming Dark Kiva (which, what do you know, Otoya dumped IXA for! Okay, at least he still used IXA later, setting up that helping hand for Wataru in the future.)
Alright, he still uses Jacorder, but seriously? I want to write the fanfic where a pissed-off Sagarc turns on him for ditching him like that. Remember when Saga was built up as being this huge bad ass? No? Also, there's some questionable morals going on here. Didn't Taiga like, kill a ton of people? They were Fangire, but they were the kind that wanted to love humans, not have them for snacks. Okay, I suppose he repents or something, but I've always sort of thought Taiga had a lot of blood on his hands by the end. I suppose you can say he goes through so much crap (losing Mio, losing his company, losing his place as STRONGEST RIDER EVER!!1!™) that he's done his time.
Despite all that, I love that 2-on-1 battle. It's retreading the 1986 stuff to a degree, but Kiva was always about that kind of repetition, so I can see what they were going for. And there's a real big explosion to boot!
Decade: So is the final battle Decade & friends vs. Daishocker's RKA, or Decade vs. the other Riders?
Going with the first one, for the same reason I love Agito's, I love this. It's kinda cheap, but that's masked by the commitment. Decade even takes it a step further though: this is pure old-style Rider action. The first word that came to mind when I saw this was "Stronger." Just like in that, the villains bring back a random collection of monsters for a final rumble out in the middle of nowhere. Some of them are even sporting the wrong weapons! I love that. The mix of Riders is interesting... hey, if you asked me to assemble a team of 5 Riders for a final battle, I would never have settled on that crew.
Of course Apollo Geist is involved so I'm going to love it. I like that his defeat was a logical extension of what we'd gotten throughout the series: Decade and other Riders teaming up to defeat the baddie, and Decade & Diend gradually going from nearly outright antagonistic to something a little more friendly. I also like that it wasn't a clear victory- Geist is the man right up to the end, only losing out because two guns are stronger than one. But they are two strong guns- Decade & Diend, together at last.
I know some take issue with Decade's final villain being a Shôwa hand-me-down, but I don't really mind, since it makes sense in a twisted way: Decade became more about celebrating all Kamen Rider rather than just the past 10 years, and in that kind of a celebration the big baddie has to be someone with street cred. For example, look at the TV special that aired after Stronger ended, that one last hurrah for the 7 Riders. The leader of the baddies, that "Commander-in Chief of Darkness" guy. Who the hell is he? (Okay, it's Hotta Shinzô IRL)
But in the story, he's just some old guy with a beard. Not as impressive as in Stronger's actual finale, with the Great-friggin'-Leader. A new villain would have worked only if they were really, really well-done. And IMHO, Decade worked best when it was kissing the past, so I think it was better in the long run to go with a villain guaranteed to be effective. And that's really all the justification I can give, because beyond that, I'm an Apollo Geist fan, so you can televise 23 minutes of him reading the phone book and I'll watch.
Also, if All Riders had been the ending was was originally intended, Decade's final villain would have been King Dark! I guess Yonemura's an X-Rider fan.
So yeah, I love this final battle. Shame about everything after it though...