I tried to like it, but failed.

Rating: 4/10 (17 May 2006)

No, I did not like this one. I liked the first---it wasn't necessarily the best animated movie, both technically and otherwise, but it had likable characters, it had soul, and it had a rhythm. Its sequel still has the characters (although it adds some that I found difficult to care about), but the rest... It becomes rather preachy in a lot of places, and too many of the lines that were intended to be funny just bombed, sometimes due to bad timing, sometimes just because the humor is awkward and contrived. That hurt the rhythm of the movie, which kills a comedy.
On the positive side, the visual humor was up to the original. In fact, it had its best moments in the scenes with Scrat, the squirrel and its indefatigable chase for that elusive nut, which involved no dialog at all, but relied completely on the visuals, and the movement. That paradise scene is just absolutely hilarious, easy the funniest moment of the entire movie.
I seems as though Scrat occurs much more frequently in the Meltdown than in its predecessor---perhaps the makers realized that their strength was animated slapstick rather than story and dialog.
So, unfortunately, the sequel ends up being a number of very funny Scrat sequences interrupted by a mostly dull and occasionally outright annoying main storyline. I'd say that if you really liked the first, like I did, you will probably want to see The Meltdown nonetheless, just to have news from Manny, Sid, and Diego---and judging by the other comments here, there is a good chance you will like it.
It's just, I didn't.