4/5 Stars. Great kids movie. Definitely the superior compared with the original. The story is better, though the mice are still dumb as bricks and can't figure out something is a puppet or a trap. The comedy is actually genuinely funny, rather than For Kids Only crap like in the first movie. The music is actually good as well, much better than the drivel in the first movie. Dom DeLuise and John Cleese are great as always, and Cathy Cavadini is perfection in her singing.
Overall, one of the best kids movies I've seen. Up there with the 1980s Disney films, just under the 1990s ones. Definitely worth a watch. If you never saw the original, it's not an issue in any real way. Oh, and the critics hated this because it was a sequel. Not really any other explanation for the bad reviews.