There are many guys who only play singleplayer and haven't experienced online play. I feel sorry for them. Multiplayer is something to play daily and more than that. One and only way to confront real humans who are certainly playing better than any AI in the world is something you can't miss.
Let's take for example CoD 4 Multiplayer. Relatively old game but despite that many will say it's the most played game today.
And without further delay I want to present you my favorite servers which you can find at Game Tracker. Vi - Net Team DeathMatch and Navy Seals Gun Game.
- Navy Seals 126.96.36.199:28960
- Vinet TDM 188.8.131.52:20000
You can follow your stats by registering here on Gametracker.