It's a tough one. I think games are better now than they've ever been, but the early 90's were my formative years. I spent many a happy night with my Amiga 500 and games like The Chaos Engine and Turrican 2 the latter having what I still feel is the catchiest theme music ever [yes]
i think you need a 1995-2005 option. That for me would cover all my favorite C&C games, RTCW, UT 99, Rome Total:War, and many many other all time favorites of mine.
I can agree with plenty of that, unfortunately that would exclude 1990-1994 where so many sweet games came out and like it or not revolutionized FPS and RTS with titles like Dune, Warcraft, Wolf 3D, DooM, and System Shock.
Not to mention five incredible space sims: Wing Commander 1,2,3 and X-Wing and TIE Fighter.
Also Super Mario World, Mario Kart, And Donkey Kong Country for some console classics. :)