For all the QQ and hate league's balance receives, especially recently with the big changes to many aspects of balance in the pre-S3 patches, I think the balance team does a good job.
There is currently only one champion with a win rate more than 10% away from 50%, and that is Karma.
There are 21 champions with a greater than 5% variation from 50%.
That leaves 88 champions that are within 5% of an ideal win rate.
Now, win rate is not by any means the only indicator of balance.
But of the 110 champions in the league, which ones are almost universally agreed upon to be overpowered?
Well, we can gauge community dislike of a champion by ban rate.
Only 4 have a ban rate about 50%
Only 7 have above 40%
"But there are only 6 bans."
Alright, what about champions the community QQs about?
There are the only 5 champions that consistently get QQ threads on the forums which get upvoted. (Recently all but Blitz have fallen off)
Malphite, Lee Sin, Twisted Fate, Even Amumu with his 66% ban rate, the part of the league community that cares enough to follow the forums do not dislike these champions enough to QQ about their balance.
Even if we take every champion with a >10% Ban rate, and every champion the community QQs about, you get 15 champions that the community is displeased with as far as thinking they're OP or annoying goes
Then there's the champions that the community thinks are underpowered.
Recently, Yi, Nasus, and Trundle have been taken off the list or something. Very few threads about them (except asking for Trundle skins) and they saw tourney play. Could they be stronger? Yeah, but they're not troll picks. (except trundle)
That's 20 champions that the community thinks are bad as far as balance goes.
If you count AD Yi it's 21.
That's 88-89 champions that the community seems to be fine with as far as balance goes.
And that is not an easy feat.
Could it be better?
Yes. Which is why Riot continues to make balance changes with every patch, and is currently doing a Karma rework.
So yeah, while you may see a lot of threads whining about imbalance, remember.
There's 88 champions that you never hear anything about. Because they're in a good place. They could be in a better place by a few % points, but if you want to play them, you are going to have a good champion and fun games.
Keep up the good work, Riot balance team.