Looking for some serious FPS combat? Soldier of Fortune II: Double Helix provides this & then some!!!
Your selection of weaponry, while not as expanded as I'd love to see all shooters to be, is plenty impressive. For realism in a shootout standpoint, it might be a few cards short of a full deck, but this doesn't deter the game from being attractive and easily addictive. Now, for realism in a gore/damage aspect, SOFDH delivers like a brutal horror flick.
Limbs removed, heads blasted off, faces knifed, bellies slashed, feet exploded, hands punctured by a bullet. It's deviously magnificent, and to this day unparalleled in it's brutality.
The single player campaign doesn't drag as much as it lacks the furious punch of the multiplayer. There's also an option to do single player side missions like an assassination where you setup certain specifications and then go in for the kill solo against bots. (Btw, bots are awesome. They should be in every game!)
So, if you happen to still have an XBOX and you happen to pick up this title in a store somewhere..buy it, take it home, and relish the visceral gameplay.