Counter Strike: GO.

[Sirion]

I prefer to play with bots because it was the very humans who made not like Counter-Strike. It's a lot harder to play it with people because there are so many hardcore players (not to say the cheaters) you hardly can enjoy the game. You just keep dying and dying and having no fun at all.

Now I have somewhat more experience in CS:GO than most (I got beta several months before pre-purchase) and understand this version better than the others. I trained hard with the bots and grew used with them. Now I'm more confident about playing with humans, but I'd still rather play it with bots, or with friends.

Casual game settings help a lot too. It's great to play without worrying about friendly fire.