As far as adults are concerned, the first 20 minutes is pretty amazing from a visual point of view. The movie LOOKS incredible. After that, the "dialogue" is bad, the scenery is weak, no real music, plot is a copy of Land Before Time (with Littlefoot).
As far as kids are concerned, my 6 year old loved it and thought it was the coolest thing ever. My 5 year old was scared to death. There are some relatively graphic, violent scenes for a kids movie. I think for kids over a certain age (maybe 5!), it's no big deal, but I think it is too scary for very little kids.
So go see the first 20 min, then leave and catch another movie that will challenge your brain a little (like Road Trip!) :)