Out of absolute boredom, and an attempt to get some discussion going, I'm going to be rating every single Limit.
Every character is at level 80, equipped with Zero Gear with three Ability Units on it. Ultima Weapon and rings are not equipped. The only reason the characters are at Level 80 are for convenience; mission mode enemies are too strong otherwise.
I'm going to use the Limits in two cases; single enemy (against Anti Riku) and against mob (against the Neo Shadows directly before Anti Riku).
Now, let's start.
King Mickey - Holy
Phrase: "Gotta win!"
Limit: Strikes one foe with a beam of light from the sky.
Final Limit: Releases a much larger version of the normal limit.
Notes: Hold A to charge up the limit to release a bigger beam. To use Final Limit you must charge beam up to max. Can not be used on far away foes.
Against Mob: 1/5
Against One: 4/5
Comments: Since it only hits one enemy until you use the Final Limit (which you have to charge anyways), it's useless against mobs. Against one person however, it's actually very powerful and very useful. Unfortunately, you have to be up close to use it effectively, so....
Sora - Ragnarok
Phrase: "Light!"
Limit: Sora fires a Ragnarok. Three small energy beams move towards targets, though one usually just goes up off the screen.
Final Limit: Sora fires a Ragnarok. Four small energy beams are clustered together and launched.
Notes: The Final Limit can go through enemies and becomes faster.
Against Mob: 2/5
Against One: 3/5
Comments: What happened to Ragnarok? Xion's version was much better then this crap. It has its uses I guess, but you're much better off using Sora's Dream Sword attack combo.
Donald - Fantasia
Phrase: "Watch this!" (Or rather "Wawth thiths!")
Limit: Fireworks explode in front of Donald.
Final Limit: Fireworks explode around Donald.
Notes: None.
Against Mob: 3/5
Against One: 2/5
Comments: It's... um... okay I guess....
Goofy - Teamwork
Phrase: "You've made me mad!"
Limit: Goofy flies foward and strikes a nearby enemy with an uppercut. Hold A to charge level two to make him go farther.
Final Limit: Goofy flies very far forward in an invincible state . This is the third charge level. Can be steered.
Notes: Goofy's Final Limit stops as soon as you directly hit something.
Against Mob: 1/5
Against One: 3/5
Comments: It's pretty much useless in mobs due to the whole only hitting one enemy at a time thing. Okay one on one, but the damage is nothing to brag about.
Riku -Darkstrom (sic)
Phrase: "You can't stop it."
Limit: Riku flies forward a short distance. Auto aimed in the direction of the nearest enemy. It's basically Sonic Blade.
Final Limit: Riku's weapon is engulfed in a large blue aura (reminds me of Lionheart). Press A to do a short combo, then again to fly forwards.
Notes: None.
Against Mob: 5/5
Against One: 5/5
Comments: Wow, how did I miss this? This move is quite frankly awesome, and it makes Riku good even without Way to Dawn's awesome special ability.
Xemnas - All-Vanity
Phrase: "You're an eyesore!"
Limit: Surrounds self in a Barrier. Ram into foes to deal damage.
Final Limit: Releases two lasers from both hands. Barrier is still active. You can use the D-pad to somewhat aim the lasers.
Notes: During Final Limit, movement speed is miniscule; you probably won't even get to move. You can not go through enemies.
Against Mob: 5/5
Against One: 2/5
Comments: Against a mob you can just charge around, but against one enemy you'll run into the issue of Xemnas's mobility (or rather, lack of it) during his Final Limit. Also, it doesn't seem to be very strong.
Xigbar - Critical Snipe
Phrase: "Had your fun?"
Limit: Combines Gunarrows together and fires. Xigbar can not move, but you can turn him around to aim.
Final Limit: Fires a large energy sphere. Has noticable recoil.
Notes: Does not subtract from Xigbar's ammo.
Against Mob: 3/5
Against One: 3/5
Comments: Unlike Xigbar's normal attacks, you can actually use this from long range. However, the recoil of the final limit can push you against the wall, where the camera will proceed to **** you up. Incidentally, the shots are blockable. It does nice damage, but you can't really effectively snipe with it.
Xaldin - Dragoon Storm
Phrase: "No" *I can't understand anything after this*
Limit: Xaldin spins his lances around him. Basically, it's a stronger Aeroga.
Final Limit: Xaldin jumps and crashes down on top of the nearest enemy.
Notes: Xaldin's jump auto target has mediocre range. You won't be able to do it from across the screen, but you really shouldn't have to do that anyways.
Against Mob: 5/5
Against One: 3/5
Comments: Xaldin can not move during his normal limit. That's kind of a problem if you miss, especially if there's only one enemy. It's great for clearing out mobs though.
Vexen - Diamond Dust
Phrase: "You're too much trouble!"
Limit: Vexen releases three large snowflakes in front of him. After a certain distance, they turn into ice pillars. Has noticable recoil.
Final Limit: Vexen summons a glacier under the foe a set distance away.
Notes: Oddly enough, you can't actually use the Final Limit on foes that are too close to you.
Against Mob: 3/5
Against One: 2/5
Comments: It's decent against mobs I suppose, but the recoil makes it kind of hard to hit one enemy during the normal limit. The Final Limit also kind of sucks.
Lexaeus - Ayers Rock
Phrase: I'll crush you!"
Limit: Lexaeus spins around to deal damage to nearby enemies. Hold A and charge to release a shockwave while you spin.
Final Limit: Lexaeus jumps into the air and hits a nearby enemy with a giant rock sword.
Notes: The Final Limit can not be used unless you hold A until there is a noticable difference in Lexaeus's battle aura.
Against Mob: 2/5
Against One: 1/5
Comments: It's really too slow to use, and Lexaeus's Y-combo does far better damage.
Zexion - Meteor Mirage
Phrase: "You brought it upon yourself!"
Limit: Zexion rises in the air and rains small meteors in front of him.
Final Limit: The meteors move faster now, sometimes land behind Zexion, and generally hit a more focused area.
Notes: The meteors are random. Zexion can slowly move.
Against Mob: 3/5
Against One: 3/5
Comments: The normal limit is pretty crappy, but the final limit is actually pretty good, as the meteors now somewhat aim. Very powerful. However, the move is useless if the enemy is behind you, or too far away.
Saix - Berserk
Phrase: "You're" *I can't understand anything after this*
Limit: Saix starts rapidly moving forward while slash the area in front of him. Press A to have him do a jumping attack.
Final Limit: Press A to have Saix jump up and release an aura around him to deal damage.
Notes: Hard to steer. Your best bet is to press A, then hold the direction you want to go.
Against Mob: 5/5
Against One: 1/5
Comments: It's wonderful against mobs, but crap if there's only one person.
Axel - Explosion
Phrase: "Don't say I didn't warn you."
Limit: Axel engulfs one of his chakrams in flame and throws it at an enemy. An explosion occurs afterwards.
Final Limit: Axel engulfs both of his chakrams in flame and throws it at an enemy. A large explosion hitting the surrounding area occurs afterwards.
Notes: As always, there is a set distance limit to where Axel can aim. Also, Axel can not move for a short while after his Final Limit.
Against Mob: 3/5
Against One: 3/5
Comments: Eh, it's a pretty decent limit, but the short time where Axel can not move after his final limit basically gives you three uses max, and that's only if you're at 1 HP.
Demyx - Wave Gigs
Phrase: "Pipe down and listen."
Limit: Press A to release a water pillar that shoots from underground in front of Demyx.
Final Limit: Mash A to release multiple water pillars before ending in an explosion.
Notes: Demyx can kind of move during this. You have to press A in time with the white flashes to do anything spectacular.
Against Mob: 3/5
Against One: 2/5
Comments: It's decent, but Demyx is too slow to really effectively use it. Try and pin the foe against a wall I guess.
Luxord - Jackpot
Phrase: "Let's even up the deck."
Limit: A card appears before Luxord. It flashes between a 'X' and another symbol. Press A to stop it. 'X' will result in the card exploding and forcing Luxord back, the other symbol will rain two beams of light on the enemy.
Final Limit: Two cards appear before Luxord. Two 'X's do the same as one 'X', a red symbol and the other symbol from the normal Limit still rains down two beams of light, and two red symbols rains down 4-5 beams of light, with the last being larger.
Notes: The move is canceled if your limit bar runs out.
Against Mob: ?/5
Against One: ?/5
Comments: This just really depends at how good your hand eye coordination is.
Marluxia - Bloom-Out
Phrase: "Sink into the darkness!"
Limit: A black circle appears underneath Marluxia. It eventually flashes pink, then disappears. Press A once to make Marluxia spin his scythe around repeatedly.
Final Limit: Same thing, only now Marluxia teleports to an enemy before attacking.
Notes: Pressing A when the black circle turns pink can apparently cause instant death to weaker enemies. Not sure though.
Against Mob: 4/5
Against One: 3/5
Comments: Eh, it's okay. Once again, the whole being forced to wait thing limits your use of this.
Larxene - Voltic Rush
Phrase: You're getting on my nerves!
Limit: Mash A and watch Larxene go.
Final Limit: Press A to cause Larxene to shoot forward engulfed in electricity.
Notes:
Against Mob: 5/5
Against One: 3/5
Comments: It's kind of weak. I mean, if there was a combo meter in this game it would be great, but it's just not strong enough. At least on bosses; it's great against enemies. I do admit it was better then I thought though.
Roxas/Xion - Event Horizon
Phrase: "You're finished!"/"I can't give in!"
Limit: Press A to rapidly attack with a large energy sword.
Final Limit: Press A to release 4 pillars of light around you.
Notes: The final limit deals more damage if you are very close to the enemy.
Against Mob: 5/5
Against One: 5/5
Comments: This move is awesome, though it's weaker then in Story Mode. Mash A and watch the opponent's health go down. Incidentally, oddly enough, Xion has a higher strength then Roxas. But then again he had a higher critical percentage and bonus, so I guess it balances out.
Dual Wield Roxas - Magic Hour
Phrase: "Give me strength!"
Limit: Roxas jumps into the air, holds his keyblades up, and summons beams of light that rain down across the area.
Final Limit: Roxas is engulfed in light and the beams of light fall faster and do more damage.
Notes: Where it hits is completely random.
Against Mob: 3/5
Against One: 1/5
Comments: Against mobs it's okay, but if there's only one enemy... well, in its defence when it hits, it hits hard.