In my opinion there are two types of overpowered champions in the game at the moment; those who are just in general too good at everything and those who just excel at a few things TOO well.
The first group (general OPs) are the ones who just don't have a downside, they usually aren't crazy at anything but they are just above average at everything without counters and just... better than others.
Off the top of my head these are the main ones, that don't have a down-side and are just stronger than others.
Ezreal, Skarner, Taric, Alistar (high elo support), Jayce.
Old Shen was a prime example of this, just the ability to do everything.
A case example would be Ezreal: He has it all for an ADC. Poke, Trading power, Steroid, AoE, Escapes, Chasing Power, Mobility, Burst, Range.
Sure a Graves is a bit tankier and has a bit more burst, but he is worse at EVERYTHING else, Ezreal is just better overall therefore.
Ezreal and these guys might not be the 100% best pick every time. for example an MF counters Soraka more than Ezreal because of a healing debuff but the point is that Ezreal will NEVER be a bad pick, neither will Skarner, neither will Jayce. They are all basically uncounterable and THAT is their issue. That is why they all have like 60% win chance, you pick them every game and they will ALWAYS be good, that is overpowered.
tl;dr: these champions are always a good pick, uncounterable (not properly anyway) and just too good all the time.
The other OP is the "situational" one. The one who you give an inch and they just pick up a team and carry them to victory. Now don't get me wrong I don't have a problem with snowballing; I love that Tryndamere or Vayne can pick up a carry a team in the right circumstances, just these listed can do it far too well far too often.
Rengar, Evelynn, Morgana, Amumu, Malphite, Alistar (jungle), Katarina, Diana (lesser extent), Blitzcrank (lesser extent)
Prime example was old Tryndamere (we all remember it *shudder*)
The issue I have with these champions is when the "right circumstances" come around too often, a Vayne will only be boss in about 2/5 games, but when she is she is GODLY. I think she is roughly balanced as she fits a niche in the game of a "possiblity" of hypercarry, but it is still situational.
I digress; the point I am making is these are the champions who have clear counters and ways to beat them, but they are often very obscure and easy to overcome; and if not adhered to these champions get ridiculous. e.g. If you don't let Rengar get fed in the first 10 minutes he will be useless, the problem with this is that is incredibly hard to do, you have to ward, stay away from bushes, get early armour and be defensive in lane. If you slip up on one of these things, a half decent Rengar will end up fed and snowballing the game out of control by 20 minutes, insta-gibbing the carry and forcing down objectives. An Amumu can be beaten by being counterjungled, if you don't do this to a high standard and if you manage to keep your lanes from getting ganked by Amumu true he will suffer a lot. But that doesn't really happen that often so most games Amumu will end up carrying his entire team on his little shoulders.
tl;dr: these champs have counters but they are hard to keep in check and go rampant far too often, the risk/reward is out of sync.
Basically both these types of champions need to be altered in order to bring them back into a similar power level to other champions. Suggest ideas below and brainstorm whatever.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.