I'd like to see a Kaiju fighting game in the style of any sort of top tier fighting game such as Street Fighter or Mortal Kombat or Tekken or whatever. And of course I'd like to see it be a crossover style game like Marvel v. Capcom, Super Smash Bros. or the upcoming Multiversus concept from Warner Bros.
Besides awesome, highly KINETIC gameplay and numerous distinctive giant monsters and other biggies you can portray who have their own extensive repetoire of strengths, weaknesses, attacks, combos and finishing moves as well as voice acting and sound effects, and of course the obligatory multiple different skins and versions etc... the game will also have utterly unique arenas with DESTRUCTIBLE and interactive environments.
Yes you can fight in Hong Kong. Yes you can throw shipping containers at people or have buildings topple upon them or trip them up into the powerlines or attempt to drown them into the bay! Maybe you can even pick up a tree and smack or choke a Kaiju!
Obviously the game will have multiplayer, it's a fighting game after all but I'd also like to see a few campaign style options. One mega campaign story mode like you've gotten with recent Mortal Kombat games which touch on every character but also maybe mini-campaigns for each character where they can fight other giant monsters but also something simple, like puny NPC enemies such as the military or whatever.
And maybe different battlemodes like a survival wave based one where you (or teammates in coop) battle ever increasing hordes of NPC's and an occassional rival Kaiju or the like every few waves, or a free for all/Battle Royale mode etc etc.
As for Kaiju to include in the game... here's sixteen I can think of.... *takes a deep breath*
Godzilla, MechaGodzilla, Gamera, King Kong, King Ghidorah, Smaug, the Iron Giant, Shai Hulud/Sandworm, Cronus or Atlas etc, Harbinger (Mass Effect), the Icon of Sin, Tiamat (DnD), Diamond Weapon (FF7), Cherno Alpha, Cthulhu and some flavor of Kraken!