The cool station is open again. It's not an igloo anymore and there's no snow or frozen caveman anymore (you know when you used to walk into it). Also when I was there in Dec. they were redoing the Living Seas (just the outside I think, you could still go in it though).
As for what else is new (I mean within the past 4 years) there's Mickey's Phillarmagic, Stitch's Great Escape (it's not that great so if there's a long line, don't bother), Soarin', Ciderellabration, Expedition Everest, Lights Motors Action (the stunt show at MGM), Primeavel Whirl and the whole Dinorama thing at AK (i think), hmm.. I'm not sure what else has changed or opened within the past few years..