Figure I might as well write up a bit about all the characters. My thoughts on them, etc.
Wizard - I hate, hate, hate his basic combo string. It's overly flashy but generally ineffective (much like Wizard himself, heyoooooooo). Kick Strike is also generally pretty useless too, unless the enemy is stunned beforehand. Water Style is zzzzz. Hurricane Style is pretty good, probably the best of his styles (just like in CH). Land Style is zzz too, but Defend is at least useful when you're defending Memory Pods and stuff. All Dragon is basically Wizard's saving grace, since the Dragon attacks are all super powerful (Land Dragon and Hurricane Dragon especially).
Beast - Er...haven't used him yet...I'll get back to you on this one.
Fourze - Plays like a Dynasty Warriors character in a game full of Sengoku Basara characters, which is interesting. His base form is pretty good, and fun to play as. I've only unlocked Elec States out of his secondary forms so far, but it's pretty good too. Cosmic States is okay as far as ultimates go, I suppose.
Meteor - Dear god, Meteor is a combo machine. Basic combo, followed by his Triangle special, jump canceled into an aerial attack, followed by an aerial special. Then just repeat the process. So much fun. Probably one of the most fun characters in the game, in my opinion. Meteor Storm is pretty good, and its initial attack does a load of damage. Surprisingly one of my favorite characters.
OOO - Not really as fun as one would think. TaToBa is okay, and his Rider Kick is a lot easier to aim than a lot of other characters', since it basically only hits directly in front of where he's standing. It's a bit disappointing that all his other forms only have one special move each. GataKiriBa's is cool, even if the duplicates are made up of like five polygons each. :lol SaGouZou's is probably the most useful, since it pulls in the surrounding enemies. LatoRatah's is super hard to aim (against bosses, I mean) and generally not that useful. But LatoRatah does have the best basic combo string out of all of OOO's forms, so there's that. PutoTyrano is decent.
Birth - Eh, not so much a fan of Birth in this game. He's slow and doesn't have a lot of terribly useful attacks. The gun doesn't do a lot of damage, and his various CLAWs aren't super useful either. His diving body press thing is good against crowds, though. And I guess he can German Suplex dudes, so that's something.
W - Not bad. Lots of forms, though none of them particularly stand out as more useful than any other, which I guess is a good thing. LunaMetal's Maximum Drive is super good against crowds. Any of the Trigger forms are generally useless, except maybe HeatTrigger, since Trigger Explosion does a lot of damage. CJX is fun, but all of its attacks have a lot of startup on them, which kinda sucks.
W Fang Joker - Honestly I'm surprised Fang Joker is even in the game. Glad he is, though. He's fast and has a lot of combo potential. Shoulder Fang in particular is REALLY good for comboing. His ultimate is a bit disappointing, but that's understandable since he didn't have any alternate forms in the show (hell, he IS an alternate form).
Accel - From what I've played of him, he's not too bad. Slow, but that's to be expected. He's got decent range for a melee character, though, and he's really powerful. Haven't unlocked Booster Upgrade yet, so I'm looking forward to seeing how that works. Trial is awesome, though.
Decade - As is always the case, Decade is super broken, simply because you can use the Kamenride cards to turn into OTHER broken Riders. :lol Ignoring that, his base form is okay. Attackride Blast is next to useless, but Attackride Slash makes up for it by being AWESOME. Fast, powerful, and combos well. His Rider Kick is really good, too. Complete Form is interesting, since it's the only ultimate form (to my knowledge) that allows you to do your initial "super move" again by pressing R2. Which is good since it's useless otherwise.
Kiva - Kiva's base moveset is boring as hell. Garulu is a little better, since it has a great basic combo string, but Garulu Bite is almost useless since it has a super long startup (the animation for said startup is AMAZING, though). Haven't unlocked Dogga or Bashaa yet, unfortunately. Emperor is decent enough thanks to Dogga Fever being SUPER powerful, but the initial attack (the drill Rider Kick) is super hard to aim and misses frequently. And the Zanbat slash is stupid as hell. Doesn't do nearly enough damage and takes forever if you whiff, leaving you ridiculously open.
Den-O - Goddamn, Den-O. Four characters in one. Sword Form is really fun, though hearing "ORE NO HISSATSU WAZA" over and over is a bit tiring after a while, heh. Rod Form is by far the most useful of the forms. Its Triangle move wipes out crowds like nobody's business, and the rod impale/Rider Kick move is great too. Axe Form is pretty good, though I wish Dynamic Chop had super armor (it really should). Gun Form is meh, and surprisingly slow, actually. Good Full Charge, though. Haven't gotten to try Liner Form yet. Climax Form is fun, and pretty powerful, too.
Kabuto - Kabuto is really fun to use, but also a bit difficult. Clock Up is fun, but it can be hard to judge how much time you have left in it, and what moves end it automatically. Having to do the "1-2-3" before the Rider Kick is AWESOME, but can also mess things up occasionally, since it's easy to screw up the button press and do another move instead. Masked Form isn't terribly useful at all, which is disappointing. It's cool that it's in, though. Hyper Kabuto is great, though not being able to Hyper Clock Up is a little disappointing. Maximum Hyper Cyclone and Typhoon are great, though.
Hibiki - Hibiki is a killing machine. His Ongekibou Rekka is so broken it's hilarious. You can just sit back all day and toss fireballs while everything around you dies. Bakuretsu Kyouda no Kata is AMAZING for combos, too. Haven't gotten Hibiki Kurenai form yet (I actually don't even remember if it's in the game, but I think it is). Armed Hibiki is disappointing, though. Best I can tell, the only difference is his basic combo string is different. The initial attack is super powerful, though. Good stuff. Overall Hibiki is great, and I'd say he's one of the best characters in the game, which is honestly shocking.
Blade - Eh, Blade's only so-so, though I haven't unlocked all his cards or Jack Form yet. His Circle rapid slash move is really good. His cards are all fairly decent, too (at least the ones I have unlocked thus far). Slash should always be on, Kick is really powerful, Thunder KILLS crowds, etc. King Form is probably one of the most powerful ultimate forms in the game, too.
Faiz - Suuuuuuper fun to play as. Kinda a combo machine, too, since his Faiz Shot hits a wide range and is fairly fast if you don't charge it. Crimson Smash is hilariously hard to use, though. Very range-dependent. Does a lot of damage/hits to make up for it, though. Faiz Edge move is ripped straight out of Climax Heroes, which I find a bit funny. Axel Form is pretty cool, though the multi-Crimson Smash seems really underpowered. Blaster Form is great. The initial super Crimson Smash is stupid powerful, and the flying Sword Mode slash is really good too. Another of my favorites to use.
Ryuki - Meh. Don't really like Ryuki that much. All of his moves save for Guard Vent have ridiculously long startup and not a lot of power to make up for it. Guard Vent is great, though. Strike Vent is more useful later on when you gain the ability to charge it, I guess. Survive Form is okay though. Still, not a big fan of Ryuki in this.
Agito - Agito's pretty fun, though again like OOO, the fact that his alt forms only have one move each is a bit disappointing. However, that said, Storm Form's special is one of the most broken things in the game. Lots of power, hits a TON of times, and has great range. Flame Form is less useful, but still good. Shining is decent, I suppose.
Kuuga - I did not expect to like Kuuga in this as much as I do. All of his forms are really fun to use, and Pegasus Form in particular is broken as shit. So easy to rack up huge combos with it. Amazing Mighty is really good, too, though I've had a few cases where the initial explosion attack would throw the enemy behind me, and make the last couple hits miss. Weird.
Overall, I'd say my top five characters are Meteor, Den-O, Faiz, W, and Decade. Still have a lot of playing to do, though, so maybe that'll change!