Which one? You know it's a trilogy, right? (Note: I was talking about the original series, so no rip-offs for hand-held machines and such.)
Wow, it's so uncomfortable seeing WoW and "really good" in one sentence. Then try the two original Call of Duty, hopefully you'll be amazed by the experience. Maybe it's a little bit rusty on the outside by now, but it's still golden on the inside.
Oh, come on ... general rule: stick to the classics and stay off the rip-offs. That being said, you can't go wrong with Medal of Honor: Allied Assault, and you better not waste your money on the latest disgraces episodes of the series.
Aside from those that have been already mentioned: the first Battlefied (1942), Return to Castle Wolfenstein, the The Commandos series (beware, HC experience!), Hidden & Dangerous, Company of Heroes, Codename: Panzers Phase One - Two.