Well, I went with Aion, after a long debate with myself.
I thought that Fallen Earth was great and all, with possibly some of the best concepts and ideas I'd ever seen in any other game, but it was unpolished, buggy and kinda ugly. So yeah, I went with Aion.
Now, a month later, I kinda hope I had gone with FE instead. I mean I haven't really even played Aion, it's just too simple for me, the different aspects of it just got really boring really quick. Maybe I'm being too quick to judge, I've been busy and haven't really given it much of a chance, but I gotta say, Fallen Earth has a lot more depth, and a devoted (and I mean REALLY devoted) indy developer team who work their asses off each day trying to better the game.
Sure, the graphics may not be the best possible, but it's really the atmosphere of the game that I miss the most. I alphatested FE since like September 2008 or something, and I have to admit that I was kind of put off by the confusing complexity of it and also the below average graphics, but in the end, Fallen Earth is the game I really keep returning to, thinking what great potential it has. It did get kind of exhausting, and the fact that the world it's set in is a monotonous desert with far less variety than the environments in, for instance, Aion kind of saddens me. But at least the game doesn't look like it's made for kids! And in Aion, though the graphics seem great and they technically are better, the realism is far lesser than in Fallen Earth, and the way they've done textures to save resources just makes the end result look sloppy. I don't know why, but I just can't seem to be able to get over that fact.
So basically if you want a mature, complex and confusing, but in the end rewarding game with a lot of depth, Fallen Earth is worth a try, I think. You can always just give up and take up Aion or WoW or some other instead, if you wish. =P