I'm a huge fan of SoF -- especially multiplayer. It's great fun, loads of laughs, etc. "Good" servers depend upon your location and linespeed, but GameSpy can help you sort that out.
Personally, I play on WON East 2, since that's the best ping I can get on my 56K.
There's some weapons that folks consider too powerful or cheesey, but that's up to one's personal preference. It's fairly easy to outsmart someone with a slugthrower or a rocket launcher. If nothing else, you can make them blow themselves up (-2 kills penalty).
I don't dig the rocket launcher, but it's just as viable a weapon as any other. Some folks hate my knives.
Hint: don't use the custom skins and disable skin downloads on your machine...there's some exploits with invisibility and custom skins. Plus, some of those downloads have contained viruses and / or parts that corrupt the game. Some private servers force downloads even when a player has them disabled, so I won't play on those servers.
Also, get your map downloads from http://www.soffiles.com . It's faster than waiting for the map to download while trying to enter the game and keeps the strain off the servers. There's other nifty downloads at Soffiles.com, like Intruder's Ping/Lag Lowerer ( a must-have for online play).
Once Sof Gold gets released (by the end of this month), everyone should be on the same version (v1.06).
Since writing the above post, I've discovered that SoFFiles.com and INTRUDER had a falling out of sorts, and his maps and files have been removed from their servers. If anyone's interested, those files can be found at WIDOWMAKER99's Page.