I agree that one level gets old very quickly, but this is done so they can test the game on many more configurations than they could ever test in-house.
For the guy complaining about the lag, make sure you set your network settings to lan/cable/dsl....the rate setting will make a huge difference for you....this is basically Quake3's netcode, so you know its good!
On my system, a p4 1.7, Geforce 3, I can tell you that this is the best looking FPS game I have ever played....the player models are amazing....
Do yourselves a big favor and check out the readme file, as this is the first game from id with different character classes....the Lieutenant has binoculars, can call in air strikes, and can issue ammo paks....the engineer can use and disable dynomite, there is a medic, and there is a soldier....and if you haven't seen the flamethrower in action.....WOW...
I really think that with the already excellent single player focus this game had, and the newly added teamplayer focus on their multi-player side, this may be a game that puts a dent into the CS crowd.....
I have read that there is some Doom3 code in this game...not sure what it is...I think it may be something with the models....but that is just me....