Took my 7-yr old girl to this and it was better than I was expecting. It's not great or anything, in fact far from it, but it does have its moments.
First of all, I didn't know it was going to have musical numbers in it. In a time where we have Moana and Frozen, your songs need to be pretty decent to be passable and the first two songs in this are so bad that I was really regretting choosing this over Clock in the Walls. Then the third song, a Queen cover, came along and not only was it really fun, but the movie itself turned around at that point and became a far better film. It maintained this momentum right until the end so overall it gets a pass for sure.
James Corden is great as a cartoony, conflicted Steve Irwin-type of filmographer. Common was actually really great as the Stonekeeper. The side characters were all good fun, in fact. Animation was better than Hotel Transylvania 3 with some nice vistas here and there, giving us a good sense of scale (important for this movie).
Good story and values too, surprising for a kid's movie that at first appeared to be ice-thin (GET IT?!). Lots of stuff going on, depth-wise, in this.
Good luck getting through the first third though. Ouf...