There isn't a definitive game. Just an opinion. I would say Vietcong: Fist Alpha.. but that's my own opinion. It is just that game has one of the most accurate physics engine for a FPS I have seen to date. The graphics are good, not great.. but pretty good and detailed. The gameplay is excellent. The weapons are the closest to the real thing you will get in an FPS, and there are many included that aren't in other games (like the M-14 with optics, RPD Light Machine Gun, and one of my personal favorites the DP Machine Gun).