I seriously did not expect “The Lego Batman Movie [1]” to be a romantic comedy. A somewhat twisted romantic comedy, but a romantic comedy none-the-less. At the same time, it's a good Batman movie, really getting the notion of his character—he is the Batman, and Bruce Wayne is the mask he wears. It also showcases the conflict between him and Superman way better than “Batman v Superman: Dawn of Justice [2] (way better—skip that movie and watch this twice).
Plot wise, there isn't much here you already haven't seen before. The Joker wants to take over Gotham and Batman has to stop him, while learning a valuable life lesson. But you aren't going to watch this for the plot, but for the humor and character interactions. Oh, and the meta humor. Alfred: “Sir, I have seen you go through similar phases in 2016 and 2012 and 2008 and 2005 and 1997 and 1995 and 1992 and 1989 and that wierd one in 1966.” Batman: “I have aged phenomenally.” Great stuff.
And lest I forget to mention it, Batman's Rogue Gallery [3], including Condiment King [4] (yes, Bunny, he really is a Batman villian) show up to help ruin Batman's day.
I was also surprised at the cameos—and no, I don't mean actors who supplied voices, but actual character cameos that showed up for the final act of the movie. That I did not see, and it was most entertaining.
So come for the comedy, stay for the shark repllent Batspray [5]. You won't be disappointed.
[1] http://www.imdb.com/title/tt4116284/
[2] http://www.imdb.com/title/tt2975590/
[3] http://batman.wikia.com/wiki/Batman_Rogues_Gallery
[4] http://batman.wikia.com/wiki/Condiment_King