I'm posting this for my friend Brian who had these gripes with GU and would like to see changes made for this game.
* Destoroyah is much smaller than he was in the movie
* Gigan 2004 should be a metallic blue, as opposed to the charcoal color he was given in the game
* Godzilla 1954's tail is much too long and thick, and also lacks the pointy tip of his movie counterpart
* Godzilla 2000's scales are too light in color
* Mechagodzilla 1974 shouldn't have bendable fingers; his dorsal fins shouldn't light up; his eye beams are the wrong color; his tail is much smaller than it was in the movies
* Anguirus' Supersonic Roar, Godzilla's Fireball, Jet Jaguar's Handclap, King Caesar's Laser Eyes, Mechagodzilla 1974's Flame Nose, Orga's Paralyzing Goo, Titanosaurus' Sonic Wave and Varan's Concentrated Blast should all be removed entirely (Godzilla, Mechagodzilla and Orga all have other powers that could easily replace the abilities listed)
* Biollante's Radioactive Sap Spray and Mothra Larva's Web shouldn't be able to create Beam Battles when they collide with a beam attack
None of the things here are gamebreaking, and I'd certainly admit that some of them are rather nitpicky. Still, I think that the game should be as accurate to its source as possible, and as such monsters should be using attacks they actually have, the attacks should look like they did in the movies, and the monsters themselves should look, move and fight like they did on the silver screen.
Miscellaneous ideas for the next Godzilla game
* Large buildings that are destroyed should come down a number of ways, depending on how they're eradicated, some sinking down into a pile of rubble, while others could topple over like a tree that just got axed--buildings that topple over do additional damage to anything they fall on, and can potentially be used as cover, or as an obstacle for monsters in chasing their opponents.
* Energy costs for each special ability could be unique, with Godzilla 2000's Atomic Ray costing three or four notches in the energy bar while Godzilla 90's could have a quicker, weaker beam that only requires two.
* In addition to health and energy power-ups, Oxygen Destroyers could be dropped that detonate after a few seconds and do great damage, not unlike a big grenade.
* While I think that the Health Cells from Unleashed were ultimately not a very good element of the game, I do think that allowing some monsters to regenerate health (Godzilla and Orga especially) was a good idea. Instead of Health Cells, perhaps you could do something like have certain monsters able to regenerate a certain percentage of lost health. For example, if Godzilla's health is reduced to 65%, he can regenerate back to 75%. If he gets smacked down to 43%, then he could heal up to 53%.
* Critical Mass designs were awesome, and I'd like to see them return, should this next game have Rage or Critical Mass return. I'd prefer it if the monsters' sizes would stay the same though.
* Alternate versions of monsters could be added to the game. Gigan 2004 could have his upgraded chainsaw form as an example. His moves list would largely be the same, but his attacks would be stronger and more sluggish. Burning Godzilla could have the same moves list as Godzilla 90's (minus his Atomic Ray, since the Spiral Fire Ray would obviously replace that). He'd basically be a superior version of G90's, only his health could drain as the battle wages on. Super Mechagodzilla, Fire Rodan, Mechagodzilla 2 (1975), and so on could all be added as slight adjustments to their earlier forms.
* Alternate outfits for some monsters could also be added. I don't mean like having Godzilla 1954 and Godzilla 1990s in GU. I mean having the Heisei Godzilla's initial character model be based off of his 1994 suit, then releasing an alternate model based off of his 1984 suit, and another based off of his 1992 suit. It would allow for a more authentic experience, and there are a lot of fan favorite suits that you wouldn't be able to cover otherwise.
* Have a Story mode and an Arcade Ladder mode. In Story mode, you could have any number of elements altered to go in the favor of the player or any AI monsters. Perhaps one battle could see Godzilla fighting against Megalon and Gigan, with alien ships teaming up against Godzilla. Another could have Anguirus in a free for all against Biollante and King Ghidorah. I don't know how you're handling your Story mode, but while you could add all sorts of cool scenarios that make specific battles more interesting, I think it's important that you also offer a generic Arcade mode in which you fight against a set number of monsters before facing off against the last boss. It seems like it wouldn't be too hard to add an Arcade Ladder into the game, so why not? Also, I'm totally just assuming that, so if there is some sort of technological hurtle that I'm not taking into consideration, please let me know!
* As I've mentioned before, a co-op campaign of some sort would be awesome. Whether it's a co-op version of Arcade mode, or some sort of co-op Story mode, or just a set of co-op missions, I think that adding some form of co-op campaign would be amazing.
* Bring back instant replays! There was something really satisfying about watching that final blow I slammed my opponent with being replayed from cool angles. I still remember one time when my friend was playing as Anguirus and uncurled from his roll as he got within punching distance from me, and then I blasted him with an Atomic Ray, sending him flying. The instant replay made that moment so amazing. The only way I could think of that would've made that moment even better is...
* ...a movie-maker mode! I'd love to be able to record and edit my battles, then upload them to YouTube. The fans could even offer a lot of free advertising by slapping their favorite matches together with some nice Hollywood-style cinematography. People would see these cool battles popping up on YouTube and inquire about the game, and BAM, another person downloads it.
* Change the Beam Battles. I don't know if you intended to have the mechanics work out the way they did in GU, but it just didn't work. I literally had to forfeit beam battles just so I could escape other monsters. If I had allies who got into Beam Battles, I'd immediately run to the opposing monster and pummel them. I could literally KO them when they're starting out 100% health because there was nothing they could do while they were in the Beam Battle.
* Ditch the RPG damage stuff. Godzilla is not weak against electricity, and more importantly this is not a strategy game, a puzzle game, a card game, or any other kind of game in which having weaknesses and resistances against specific attack types makes any sense. It just gives certain monsters arbitrary advantages or disadvantages over others. Take Godzilla and Ghidorah in GSTE. They're more or less equally matched, but Godzilla Atomic Ray does crap damage to Ghidorah, while the three-headed monster's Gravity Beams can utterly destroy Godzilla because they just so happen to be a specific element that Godzilla can't take. Also, MOGUERA is weak against EVERY monster in that game, except for the Godzillas. I don't understand how that's fair. It's like having Scorpion's fire-based moves in Mortal Kombat doing extra damage against Sub-Zero. That would be unfair. These battles are supposed to be fair contests, unless there are specific handicaps in place such as story-related hindrances on your character. I don't understand why you'd permanently handicap Godzilla when fighting against Ghidorah, even in what should be a fair and balanced multiplayer fight.
* Allow for CPU battles. It shouldn't be that hard, and if unlocking content is tied to all game modes as it was in GU, then simply disable the unlocking part when no human players are involved in a battle. While the battle is being waged, you could even allow whoever's watching to move through the match as a ghost camera. Oh yeah, that reminds me...
* ...add a spectator mode. As I just mentioned, spectators could take control of a ghost camera and move around freely during the battle. This could even be tied into some sort of 'king of the hill' mode where a party of people could get together, and the winner of the match competes against the next person in line, and so on.