It depends on your preferences. Do you value story or characters? If yes, it's not worth it (not to spoil you), the story goes over the edge and it gets really ridiculous. When you have a series with time traveling, future sight, and all sorts of stuff, it makes the series difficult to end logically. I suck at explaining. This show is gorey and more of a guilty pleasure for me personally. I watched it once and never going back again.
Ask @Dream: since he reviewed Future Diary. He's more articulate than me.