I wasn't disappointed with the ending as some of you seem to be.
First of all, I thoroughly enjoyed Under the Dome. I did however think it could be 200 pages shorter. I started skimming after page 350 and things picked up again around 500.
I wonder what it is like to be the editor for King. I'd be scared to touch anything. I highly recommend it. It is, as others have stated, vintage King. I think my favorite is still Salem's Lot (but then maybe that's why I wish UtD was shorter!).