I'm saving up for Mordekaiser. I know, I know. I missed the boat on that one. But I don't care.
1) I don't like overpowered champions. No matter what people like to complain about, the game's in a pretty good state of balance. Vlad's not that much of a problem (although his design is absolutely awful, in my opinion), Pantheon's not so bad if you build some damned armor, and Kennen's not even all that. All three of them are certainly strong to be sure, but not overpowered.
2) When Mordekaiser was overpowered, he was absolutely uninteresting. I know the arguments for and against his former overpoweredness, and I was always on the side of "he's not overpowered if you quit standing next to him in your own creep wave", but still. He was, by anybody's standards, an improbably strong laner, and that's just not interesting. You don't win lanes against Morde, you just let him push to tower and then farm under the tower. How that was considered good champion design was beyond me. But there couldn't be anything more boring than a giant deadly wall of death and spikes.
3) You saw him on both sides in every match (at least in Normal games) and that, again, just isn't interesting. Everybody would complain about him being OP as they stand next to him and try and poke him to death while not building MR. Geniuses, every one of them.
4) I'm a metal fan and anybody with an ability named after Megadeth songs is cool with me. Metallica is lame, but Megadeth and Black Sabbath are absolutely awesome.
5) I need another farmer for when I'm bored with Sivir. I really like Sivir but sometimes there's no room for more attack damage (like when my lanemates decide to pick Trist, Yi, and Warwick. Oh, thanks guys.)
That's about it. Keeping up with my writing practice has never been harder when you want to play LoL all day.