Originally posted by: WhipperSnapper
The greatest FPS ever produced is the original
Unreal Tournament (1999). (Yes, the original is widely regarded as being far superior to the attrocious UT 2003 and the merely tolerable UT 2004.) The game played well online and it was open to modders who created many different game types and also mappers who created, literally, thousands of custom maps. Unreal Tournament capture the flag online is by far one of the greatest FPS games ever created.
If you're open to playing an older game that lacks modern day eyecandy but that still has good graphics and exceptional game play, find a copy of the Unreal Tournament Game of the Year Edition, learn how to play it, and get online. The game doesn't have much copy protection or keys, so you can easily buy one off of eBay for a couple bucks.
I recommend this server and community for beginners:
Server name: UTCTF.thegamebox.net
Community:
www.thegamebox.net/forums