I had an odd reaction to this. The design and style of the thing was so close to the animated series, but the change in voice cast just sort of pulled me out. It was like someone pantomining the Animated Series corpse. In particular I could hear, exactly, how Hamill's Joker would have read the Joker's dialogue in this and it just distracted me from DiMaggio's performance. I get that he was trying another take on the character but it just really seemed to lack oomph, definitely my least favourite Joker interpretation.
Greenwood was bizarre as Batman, just a full on Kevin Conroy pastiche. I actually thought Jensen Ackles was the bright spot, voice acting wise, probably because I didn't have any preconceived notions of the character. I also liked Jason Isaacs as Ra's Al Ghul, largely because I just generally like Jason Isaacs.
The tone seemed off to me as well. Whilst I appreciated the choreography and the weight given to action sequences, I found it perhaps a little too 'grim-dark'. I guess if you're adapting, partially, A Death in the Family you can't avoid the Grim-Dark but it came across as a little much in this.
I actually thought more family orientated films like Mask of the Phantasm and Return of the Joker were more 'adult' in their tone and content than this.