I just watched Ice Age: The Meltdown over the weekend with my kids. They seemed to like it, although I really didn't. I thought it had some funny moments (mostly with Scrat), but was mostly nonsensical. Stream of consciousness in movie form comes close to my impression.
What really struck me, though, was something that appeared briefly before the movie even started. It told me that the people who did it were the same ones who did Rio (which my kids and I both love).
So I was really surprised when the movie started, and I just found nothing compelling about it. The whole thing just didn't make a lot of sense. Melting isn't that sudden, and an ice dike can't be strong enough to hold back that much water. So the whole premise was a bit cock-eyed. And those proto-sharks, whatever they were, were really pointless and silly. And, to top it all off, escape via deus ex machina.
I wouldn't say it was terrible, but I certainly wouldn't say it was good. Now I wish I had the first movie, because I remember that one as being pretty good, but nothing more specific than that. I suppose I'll need to see about getting it, now.