The Lego Batman movie is way, way better than it needs to be. Hanging off two solid franchises (the clue's in the name) it could confidently expect to make a fortune just by showing up. At least for one episode at least.
However, it is very, very, good. Just the right balance of action, story and knowing self-reference to keep everyone happy. I don't think I've laughed out loud at a film so many times for a while.
Very strongly recommended.