As a first-person shooter, Return to Castle Wolfenstein pits you against hordes of Nazis and Occult opponents. In a race against evil and time, your goal is to blast your way to finding out what exactly the Nazis are up to in Castle Wolfenstein.
I was at first highly amused by RTCW, but unfortunately my enthusiasm faded quite fast. Nothing really wrong with the game, but I found that the level design went downhill and got generic very quickly.
By comparison, it's silly, but I actually prefer something like Serious Sam, as a shooter. It's got more interesting things going on than what transpires in the single-player mode of RTCW. So while I respect RTCW for its control, framerate, and occasionally its level design, I wish there'd been fewer ho-hum levels to keep it fun. Instead, it got old to me and I traded it in.
Also, a side note - like most people, I do not have Xbox Live. The multiplayer aspect on Live (if you're into Multiplayer shooters) could be a different story entirely.