Aimbot does make it fun, but only sometimes.
Horrible servers? Well, in there Aimbot sure is fun. But on a great server, aimbot is not fun.
I remember me and my friends always used to hack on CSS servers, it was so fun, they all were mad. But did we do right?
We did, I'll tell you why; They all were cracked servers and none were legit. Besides, they didn't have even the most basic admin to protect them. The servers we were on were horrible.
I don't know about BattleField 3. I'm sure it's exactly like other multiplayer games = Find a good server, favourite it and never stop playing on it.
The only game where I found 0 cheaters is Killing Floor.