I have been playing online games for PC for like what, 5 years or so. There are however, many reasons that i don't feel as inclined to play online games anymore:
1. Bad communities - they may have heaps of people in them, but when all these people are complete wankers, it isn't really that much fun. Counter-strike is probably a great example of this. The game is ok, maybe even good, but when coupled with a bunch of campers and elitists, it's easy to see why it has such a following of haters. Those 10 year olds kids yelling into their microphones don't help either.
2. Repetitivity - It is cool when you first start playing games online, but after a while this "cool i'm playing against actual people" becomes pretty dull. Also, see above point for reasons. The originality of new online games is also slipping.
3. Everyone wants to be "the hero", but in online games, you realise you're just another nerd playing a game online.
4. Lack of co-operation: closely tied with point #1, there is no point making team based games when everybody plays "Lone Wolf"
So in conclusion, the only game worth playing online is DOOM II. The best way to play this is dialing up directly to their modem. Co-op of course.
P.S. This is about online PC gaming, console online gaming may not have the same problems.