I think the only major misstep (in terms of what they built) is the winter scene. It takes up a ton of space, lasts forever, and basically nothing happens. The rest of the ride ranges from okay to good, even though a lot of it could be easily improved. They should have showcased some other things -- the winter scene would be significantly better if you started out in the library and then moved out into the snow for a shorter period of time, just as one example.
I'd still prefer having it added to Fantasyland at WDW than TRON to Tomorrowland or Ratatouille to EPCOT, though, if I had to make a choice. I'd rather ride it than the other two. That's not to say I'm mad about either of them coming to WDW; it's just if I had to pick one of the three it would be BatB even with its flaws.