I judge the best environments to be the best examples of an environment. As the years progress the realism and atmosphere of certain games gets better and better. For me, it's those factors that have decided upon the greatest environments, and I can narrow that down to the following three games:
1. Bioshock - The Americana, 50's city dowsed in fear and ocean.
2. Fallout 3 - Post-apocalyptic destruction with struggling survival and limited water
3. Red Dead Redemption - Western brilliance complete with music stings, wild animals and desolate beauty. This game has the best environment in my opinion, despite that in real life I hope to never visit another desert again. I hate the heat and the searing sun and yet RDR makes me want to move to Colorado.