The AMC at DTD is amazing. Catching a flick is a great thing to do if you aren't feeling especially adventurous on your first night, and just want to relax but not sit in your room. For those that don't live near big city multi-plexes at home, it also can just be a treat to see 24 screens under one roof. It can also be a great idea for those who love to shop - the rest of your party can be entertained for a couple of hours while you shop DTD. This way it doesn't feel so much like splitting up.
I hate to plug another park (hehe), but the theater at Citywalk is also very good (off the top of my head, I can't remember - is it Sony?). I saw Moulin Rouge there and the sound was spectatular. It's also very conveniently located - it's pretty much the first thing you hit when you get to the end of the parking area and reach CityWalk.
Would I spend a great deal of time watching commercial films? No, but on days when you aren't doing parks and would just like to sit in a nice, air conditioned theater that WON'T spray you with water, make funny smells, or otherwise attempt to stimulate every sense for maximum effect they can be very relaxing.
N.E.D.