Theory: Batman alone is tragic. Batman in a teamup is cool. Batman in a league: AWESOME. If Batman the Animated Series is the soul of the DCAU, where it first got its legs and took flight, here is where it grew up and became so much more. The depth and humanity displayed in full-length movies such as Batman: Mask of the Phantasm is here in most episodes (there are, as always, a few misteps. Hawk and Dove is one that stands out, mainly for being exactly the wrong kind of ridiculous.)
Do you have a favorite character in the DCU? You'll probably get something out of them here!
If you don't know the DC universe, if you don't know Batman or Superman at all, perhaps you should start with Batman the Animated Series. If you do know them, at least a little, you won't go wrong by buying the DVD collection if you want a great action show with fun characters. Not for kids, but nothing more than PG-13 material. Thats my 2 cents.