I mean all types of envoironment not only big ones like crysis.
Do u guys think that Gears of War 2 could mantain the same graphical quality of the first one while having alot more interactive environments?
If by interactive you mean destructible, as in see a wall, tree, house and blow a hole in it or raze it to the ground, then there are two issues. The first is of memory. Everything you do needs to be stored somewhere, so indiscriminate destruction rapidly uses memory as you have to store all the damage that has been done and the new models that are generated as debris or whatever.
Secondly, you're going to be generating more polygons, so either the game will suffer slowdown, or the levels have to be designed with a budget each frame to account for any polygon/detail increases which take place. So let's say in GeOW case, either everything gets uglier to save on poly counts and memory to allow the destruction, or destruction causes the game to begin to stutter.
There's also a hit on the physics system etc if you're going to realistically model the debris, but not so much.
You can special case it (i.e. have a set number of 'debris' objects spawned whenever something happens) but players see through this quite quickly, as every destruction looks the same.
If you're taking this destructible environment online, then you have to transmit all of this data to every player, things could get out of hand very quickly. That's why truly destructible environments are a rarity, and that's before we even go into the whole "what does it add to the gameplay/how to we prevent the player doing something unexpected and ruining our scripting etc" arguments...