I saw this movie on Saturday 3/27 with my tween daughter. We both enjoyed it very much. The story was good, clean, family-friendly. No movie is worth seeing if it can't offer those things.
The IMAX experience was worth it. Usually, we see 3-D movies and are let down, and wish we'd just watched the 2-D version, but How to Train Your Dragon was a great 3-D experience.
I think it also offered some good moral lessons. It was worthwhile to see, and very entertaining. GO SEE IT!