Just bought it and watched it last night with my kids. They liked it, but I was a little disappointed. It had a lot of clever humor as one would expect, especially some "inside jokes" for comics fans.
However, I thought that it wasn't as good as The Lego Movie. The running gag throughout that film was the obvious: Everything is made out of Legos. Almost all of the humor, plot devises, jokes, etc. stemmed from that fact.
Yes, everything in Lego Batman was also made out of Legos but it wasn't a major part of the plot except for the final scene and a couple of instances of Batman building things along the way. Honestly, there were a periods of time lasting almost 20-30 minutes at a time when I completely didn't notice, then Batman would build something out of the pieces of his environment, and I would get that "Oh yeah, right. I forgot. Everything is Legos."
But... the kids liked it and that's all that matters to me I suppose.