Well, I just finished it and... WOW!
It's possibly one of the best sci-fi series I have seen (and I'm not just talking about anime here). It starts a bit slowly, but things start to pick up at chapter 4 and after chapter 12... well, just WOW!
It has its share of weirdness (mostly provided by the rather excentric cast of characters) and the plot can be a bit difficult to follow at times, but it never really crosses into the confusing, labyrinthic, mind screwing mess that many other stories with the same theme can devolve into (I don't want to spoil anything, I'm just going to say that it has to do with time travel and time manipulation, so you can guess what kind of stories I'm talking about).
Guys, you should really see it if you have the chance.