No space marines. No WW2. How about just no marine/soldier theme in general. I'm not a big "violence in video games is bad" banger, I just think it's boring. And it's not my fantasy. I don't want to be a fucking soldier, shooting people is horrible, why do you want to pretend to do that?
Not gray or brown. Give me some damn color and beauty. I want to be excited to see the next level, and I want to be surprised and blown away and delighted when I do. There are endless possibilities for fantasy worlds, you can do better than warehouses.
Not primarily about combat ; especially not repetitive combat, like shoot these 20 guys, okay now shoot 20 more guys. Bleh, I'm bored.
Not "Don Bluth" semi-interactive , ala "Press A now" - you pressed A! good for you, monkey! (I'm looking at you, God of War). (actually I kind of liked those games when I was a kid even though it was uncool to like them; my favorite was "Cliff Hanger" which I just learned is actually a Lupin The Third movie!! crazy, when I watched Lupin a few years ago I didn't make the connection)
No giant inventory trees or management games or spread sheets; I do work when I'm working, I don't need to do work in my game.
No abstract puzzle games. I'll play chess or go or something if I want that.
Absolutely no frustrations. Long load times or annoying UI or one bad level that gives me instadeath for no reason - the game's going in the bin. If the game makes me scream at it or grind my teeth in frustration, I don't need that in my life.
My favorite games are generally "light RPG's" like Faery Tale, Zelda, Drakan, where I get to run around a big world, but without a bunch of fucking dialogs, and without managing a big group of characters and stats and such (I generally love true RPG's for about the first quarter of the game, but then you get too many people in your party and too many items and spells and it just becomes a huge pain in the ass).