I just watched it, and after getting only 10 minutes into Superman: Unbound,  I did not have high expectations.  However, I ended up really, really enjoying it.  More than anything, it's a film with consequence and heft, where I felt the impact and cost of death.  Barry Allen was the most interesting I've ever found him (I've always been a Wally West guy) and all the characters were filled with purpose.  Overall, the top 5 DC Animated films are:
1.  Batman: Under the Red Hood
2.  Justice League: The Flashpoint Paradox
3.  Wonder Woman
4.  All-Star Superman
5.  Green Lantern: First Flight