After playing NOLF2 I would have believed you. But the latest Monolith game I played was called FEAR.. Now that's the exact opposite of diversity. GREY GREY GREY!!
Well, I think diversity can mean many things. For me, it's certainly not jumping from a desert into a jungle into an office building into an underground parking area.
And the colors in FEAR were properly. No crappy bright and colorful nonsense there, only beautiful Art direction, wherever I looked at (and yes, I actually did like the blocky structures too.... made the enemies look more like they stood out of the background). Though the coolest thing was the smart combat AI, the sound design, the fun combat, the slowly evolving plot, the nice audio logs. All these things that kept me enjoyed and concentrated until the last level. Something that so many other FPS creators (id, Epic, Gearbox) just don't get right. They can have better graphics and more level design diversity and more enemy diversity...it doesn't matter to me, these games still bore the crap out of me.
Funny though that nobody ever complained about Thief's "diversity"...