Another one:
Your standard simple arena fps game but with a twist: there are literally hundreds or thousands of different weapons in the game that do many different things, and the weapon spawners on the maps would just randomize the weapon every time it respawns. This would make getting to know the weapons much more difficult, but I think it could be some silly fun. And if you happen to manage to do this, you could memorize the look of each weapon to correspond to what each does because each variant will look much different from each other.
And because I'm bored here's some examples:
A homing rocket launcher that is however weak
A shotgun that you can charge to fire more pellets but at a higher spread
A powerful but slow rocket launcher that you can accidentally hit yourself with if you walk forward while firing it
A railgun that teleports you to the player you killed whether you want to or not
A ballistic rocket launcher that bounces 5 times before exploding
A railgun that fires in the opposite direction too, with the back shot instagibbing
A rocket launcher that fires upward, like Danger Wrap from Mega Man
A rocket launcher that fires invisible rockets, but has a bright glow on walls
A burst firing ice launcher that slows people down a bit
Many things from TF2
Many things from Mega Man
Many things from already existing weapons from blockland
