"To be honest, I'm not sure I've earned the right to wear this uniform. But I will."
Superman/Batman: Apocalypse is a decent animated adaptation of what I think is one of the better modern DC crossover stories, The Supergirl from Krypton. Basically, it's the introduction to the newest Supergirl, Kara Zor-El. Kara's discovery, training with the Amazon's, abduction by Darkseid, and the aftermath are all depicted, if in a severely abbreviated version. The story features all three of DC's most iconic heroes (Wonder Woman joins the two title characters), as well as Darkseid and a smattering of lesser known heroes and villains.
The animation is okay (but not spectacular), I had no complaints about the voice acting, and as I said, there is already a great story for this movie to use as a template. But it's so brief that important events speed by with little time to develop them or the characters. The movie finally rounds into fine form with the exciting finale, but overall you'll have a more satisfying experience from the comics. Superman/Batman: Apocalypse will serve if you just want a little over an hour of DC action on your TV, as it's pretty action-packed and doesn't last nearly long enough to be boring.
For parents, as with other recent DC animated movies, this is aimed more at older teenagers and adults than younger kids. There's mild profanity and a healthy amount of violence, so keep that in mind. Nothing too extreme, though.