I liked pretty much everybody in Blade, but then it sticks to the "Riders = Good" thing, so I would (let's just overlook Missing Ace for the moment.) Even though everybody gets a chance to play "bad guy" at least once (Crazy King Form Blade, Untrustworthy early Garren and Chalice, Leangle for most of the series) in the end everyone's ultimately a hero, if plagued with issues. Kenzaki's the most reliable, trustworthy of the four and even he gets called into question at times during the show. But I never for a moment questioned why the show is called "Kamen Rider Blade", either. Like Agito, it's a multi-Rider show that did a good job balancing out the Riders, but reminding you why it's named after just one of 'em.
I cut Mutsuki a lot of slack because he's a combination of two admittedly tough tropes to work with: the whiny, impulsive new guy who thinks he's the best thing ever, and eeeeeeeeevil possession that makes you dress in black. He spends most of the show as one or the other, and they play into each other. He starts as the clueless average joe who's secretly the most powerful Rider of all*, so Tachibana takes him under his wing. Tachibana himself is a bit of a screw-up though, so of course it goes all wrong, and the evil Spider Undead influence takes over again.
*I know, not really, but this is standard-issue STRONGEST RIDER EVER!1!!™ logic here.
I'm still not sure how that whole Shima/Tarantula Undead thing works out, since it always appeared to me that it failed and resulted in black-dressing, card-playing, nightclub-lounging, Joker-assaulting, cop-beating-upping emo Mutsuki. But since we do get the eventual payoff, I tend to chalk it up as a long-term plan. I'm not sure, but I'd like to think that Imai intentionally left it hanging at Aikawa's request to get back to it later once the Tiger Undead thing had been played out, but I dunno.
All that said, I liked how he turned out. It helped that I liked the final result (a humbler Mutsuki just trying to do the right thing when everything is going to hell around him) and that Leangle was pretty cool. And after all the ID-switching business of Faiz, the one time they did the "another guy becomes the Rider!" thing, it was awesome. Crazy as hell, but that's Inoue for you. Electric robot arm indeed. (Those episodes are another time where you can see my "Being Unsealed Makes You Crazy For A While" theory in action, IIRC.)
Blade's a really hard show for me to find fault with. I remember that in 2004 the early signs made it feel like a "Greatest Hits" of Heisei Kamen Rider thus far. Another ancient race wakes up to kill people yet again, and they also happen to be more of the unliving. Yet more card-wielding Riders fight them, and once again we've got more than one (this is back in the days when everybody secretly sort of thought we'd return to a single Rider series eventually.) There's a bunch of other superficial complaints offhand I can't remember.
Of course all that's true to an extent, but I think Blade actually took some of those ideas and improved on them. The Undead are a big one, scoring high in my book for three main reasons: 1) the excellent designs that cleverly nod to the past whilst still feeling original, 2) a meaty, high-concept idea and diverse motivations that still sort of weave together, and 3) Isaka. Dear God, Isaka. I don't think Kamen Rider has had as good a villain since him, apart from Tendô. Oh relax, I kid, I kid. I mean apart from Apollo Geist, and he's basically just the Shôwa version airlifted in to give Decade some real menace since Narutaki failed on all counts there. Of course he'd be awesome. Alright, alright, Kiva's main villains were cool and Mick makes Double worth getting up for. But seriously? Isaka's the man. He did something which blew me away in 2004 and still blows me away today.
His evil plan actually worked! Admittedly, not in the way he intended, but if you think about it, Leangle is his doing. As much as Leangle is the Spider Undead joyriding around to wreak havoc, it's also almost Isaka's sort-of revenge from beyond the grave (or card.) I love the early Blade episodes and the whole arc of Isaka culminating in Leangle is one of my favorite parts of the show. Let's not forget he killed off a kinda-big supporting character as well. It seems that lately the death toll only rises near the end, aside from villains/pseudo-villains. Can you imagine if the next Double ended with Watcherman being force-blasted to death? (Okay, bad example, but you know what I mean.)
And there's the Trials. I love them. One reason I think the Undead worked is that there was a set number of them from the start, and we don't even see all of them over the course of the series. As a result, they just seemed a bit better characterized than the monsters of the week in some other shows, because there was a real effort to make them distinct. They're true old-school baddies, a throwback to the days when Kamen Rider episode titles were named after the villains. I can tell you what Locust and Moth Undead were like; what they did, which Riders fought them and why. The only thing I remember about Barnacle Orphenoch is that Takumi turned into Delta to kill him. And he had a ball.
So the Trials could have been a big disaster. Adding in more Undead, and phony-baloney ones at that? But they rocked! It helped that they're actually tougher than the real ones, necessitating King Form and Wild Chalice action, but in a way also weaker, since they actually die. They're getting back to the "science run amok" thing Blade had going early on. Sure, it's the science of fantasy ("I took this DNA from you Tachibana and made... that guy! He's got a green Faiz's sword, see?") but that feels right. They also have some of the best designs out of an already well-designed group of villains. I just wonder what happened to A & C... Decade missed a trick there, methinks.
Moving on to the cards, which I think were done better here than in any show before or since. The Advent cards are cool, but they're just one of the crazy ideas thrown into the Ryuki blender. They're just there as a neat way to summon the weapons/powers, but they could have just had everyone using pocket mirrors to accomplish the same thing, and that would have made more sense. Or heck, just be like "Gimme mah sword" and there it is.
Pretty much the same thing with Decade, though those cards had the added features a little thing I like to call "in-show branding", wherein you put words and icons within the show without actually having (or requiring) an explanation. Like, why does Ichimonji's Henshin Belt have the Tachibana Racing Club logo on it? Who knows, who cares, it looks awesome! We never get Tsukasa stopping and going "Wait, why is the green Kuuga called Pegasus Form?" He doesn't, and we don't question it because we know that's what it is anyways.
With Blade though, they went a few extra miles, weaving the cards in and out of everything, from the Rider's motifs and civilian clothes (the jewelry, which is brilliant in its subtlety.) They pulled from not just one deck of cards for inspiration, going into the tarot as well. I love that. If you really try to examine it, no, it makes no sense why the ancient battle for domination of the Earth would result in the world's most dangerous trump. But it's a great idea. I also like the way the powers of the cards worked, in that they managed to keep them all internalized. Only when upgrading to a new form do we get physical changes to the Rider/Weapons. Sure, Bandai made a couple bucks off "pre-Rider Kick" variants where Blade's Spade-face is painted red, but hey.
I could go on about this show forever. It's one of my all-time favorites, and that's some pretty tough competition these days.