You're out of ammo!? Then scare 'm to death!
The rich levels, though linear, are enjoyable by spying on your opponents and, listening to what they talk about and then, what I like to do, give 'm a nice head shot! There are times that sneaking won't work and the good old run-into-the-room-like-an-idiot-and-shoot-every-frecking-nazi is really a great relief.
The further you get the 'darker' the enemies become: Skeletons, mummies, demons and other sorts of your not very average playground visitors.
If you are a fan of multi-players be sure to to download "RtCW - Enemy Territory", it's for free!