_{(this is the unfinished, sketchy version. I will eventually finish it)}
The full, extra long title:
Monsters vs. Aliens vs. Zombies vs. Pirates vs. Ninjas vs. Vampires vs. Cowboys
I call it "MAZPNVC".
What is it?
Well, to start, you choose your "team". Then you choose which "team" you're going up against.
Next, each "team" has it's own style of play:

• Monsters: ??? _{(I don't know yet. You can give me ideas!)}
• Aliens: Scrolling Shooter
• Zombies: RTS
• Pirates: Adventure Game (a la Curse of Monkey Island)
• Ninjas: Fighter
• Vampires: Metroidvania
• Cowboys: FPS

Next, you choose whether you want to be "At Home" or "Away":

• At Home: You play with your own team's play style. i.e.: Pirates vs. Cowboys at home would be an adventure game.
• Away: You play with your opposition's play style. i.e.: Pirates vs. Cowboys away would be an FPS.

And then you go into battle! Each scenario will have it's own unique story and levels. You'll be able to set the difficulty, too.
Each team will have many characters (or types of characters, where applicable) to unlock as you progress.
I also thought of mix mode, where you are given a series of random scenarios of increasing difficulty.
Multiplayer would be obvious for this as well!
Some other games that have tried to include many types of games end up with some games better than others. But I want to make sure that each game style is equally enjoyable. Some people might like some different than other people, but that can't be avoided. Everyone will have their favorite team (or teams) to play as!

What do you think so far, and what ideas might you have? Thanks for any suggestions or ideas!

I'd play that

Thanks!

What about a Slime class? You could roll around in a top down world, eating your enemies to grow and get stronger.

That might work for a kind of monster... maybe the monsters should be a top-down rpg type game?

I think the monster should be a turn-based strategy like Fire Emblem. I

This sounds cool.

And I agree with this... I was actually about to suggest that.

Sounds good to me!
Next, I'll be drawing some concept art for the actual game!

And, I also thought of this: Maybe you could also choose the time and place as well?
All of the locations associated with the various teams would be included (The Wild West, Transylvania, Post-apocalyptic City, Haunted House, Graveyard, etc.), but maybe also include some outlandish places that don't fit any of them? Like, how about a steampunk world? Or various places from history?

I'm thinking about adding Secret Agents, too.

surrvival horror would be a good fit for monsters.

Maybe you could also add ghosts and dinosaurs!