Nasus, the Curator of Boredom
I've always hated Nasus as a champion, and no, it's NOT because I think he's OP. I want to make that expressly clear. No, I think Nasus is guilty of another crime, and that's being boring. He's boring to play as, with, or against. He seems almost designed this way.
His EXTREME reliance on farming means that he sits out most team fights, opting instead to stay in top lane farming Q stacks. This creates an obvious disconnect between Nasus and the rest of his team. They aren't the unstoppable force of blue/red team, their blue/red team plus Nasus. Having this champion in the upper left corner farming and denying any engagement thanks to his Wither is simply frustrating and not fun.
This is, of course, until he's reached what he believes to be an appropriate number of stacks, whereupon he will walk up to your towers, Q them a few times, and then they're gone. Team Nasus strikes again. The turrets are designed to be strong enough to require coordination from the enemy team to take them down. This is, again, to promote tactics, communication, and fun. It seems utterly BACKWARDS that this player is being rewarded for NOT playing the game, and instead sitting and waiting while everyone else has had to work to become powerful.
I've had a friend tell me that he likes Nasus because he's the ultimate comeback champion. As long as he's on your team, there's always a chance of wining if the game can go on long enough. He's right, but I don't see that as a good thing. Having a Nasus in the game almost exclusively results in a 50 minute death-march of a game. Regardless of whether the team with the Nasus on it wins or loses, it's going to take forever.
As to fixing this problem, the only thing I can really think of is removing him from the game, honestly. It seems strange to me that Nasus isn't the only champion with a stack mechanic (Veigar, Thresh), and yet he seems to be the only one with this problem. His Q stacks are already doubled if it's a champion being killed instead of a minion, but that seems quite disproportionate considering how much easier it is to kill a minion. Perhaps reducing minion stacks and increasing champion stacks would help draw him out of his corner? Maybe get rid of minion stacks altogether? Let me know what you think.