Well, I think I'm more of a fan of the form upgrades being a really drastic change. I like Blade King Form or Armed Hibiki for that reason- they're different enough from the original design yet still recognizable as the character, and much more of a change than "inbetweeners" like Blade Jack Form of Hibiki Kurenai were. The flip side to that is, at least with Hibiki Kurenai, I felt it had a better in-story reason for being in the show than Armed Hibiki did (I prefer the movie version of that one) but since we're talking about designs here, I'll stand by what I said. The exceptions I make with this is with the old Riders like Rider 1, 2, or Skyrider changing, but those were really more of a permanent costume change. And with Agito Trinity Form, which is basically just Grand Form with the arms of Flame & Storm, but it always felt to me like something they were building up to from the start, with the asymmetry of Storm & Flame Forms, and I'm actually bummed they didn't use it more.
Faiz Blaster just felt kind of like "we always do the supreme final form so we need to do it here too" and not really anything amazing, especially after a neat idea like Accel (which really could have been done without even changing the costume, IMHO, but then I guess Clock Up wouldn't seem so special now.) And it's really not that different from the regular Faiz I felt- they changed the armor a bit, and he has a jet pack, but the weapon itself could have been used by normal Faiz and it would basically be the same thing I think. But you can say that about King Form or Armed Hibiki too, so I guess it just boils down to what you like. (On that note though, the Faiz Blaster Souchaku-Henshin figure is possibly one of the best Faiz toys ever made. I collect some of the toys, so I generally also think of it from that angle- "Is the new form really neat enough to warrant buying?" I usually skip on buying the add-on forms unless, like the Blaster figure, they're really cool.)
The thing about the Kuuga ones, mainly the Rising Forms, that bugged me is they were just too close to the others to really feel needed. They slapped some gold paint on here and extend the weapon there, but all they really needed to do was strengthen the existing ones. I cut Kuuga some slack since it was part of the plot, of him getting ever stronger until Ultimate Form, but I think it would have been more effective to just drag out introducing his regular alternate forms for more of the show, or make the current ones stronger without actually having to change the costumes, because, like with some later alternate forms, the costume change is really so slight, I don't think they were really needed.
I do like the default Mighty Form a lot, but I feel the umpteen others kind of cheapen the whole thing overall. Dragon, Pegasus and Titan I like okay, and Growing is neat in theory (I would have liked it if they went further with it and made Kuuga even less armored.) but the way it becomes little more than a way to show Kuuga just got his butt kicked...It's like if they had seriously considered the "Power-Down" short-horned version of Gills as a seperate form (maybe they do, I dunno.) or had Ryuki go back to Blank Ryuki all the time. I already said how I feel about the Rising Forms (and Mighty Rising goes with them.) Ultimate Form...I guess I wish it had lived up the hype, because as cool as it was, it was just so seriously underused. Design-wise though, I like it, but the original Mighty is still the best Kuuga to me.