In the wonderfully time-challenged world of animation, Earth's most recent, 40,000-to-100,000-year-long Ice Age is over. It seems like just yesterday-or at most a few years, judging from one flashback-that Manny the mammoth (voice of Ray Romano), Sid the sloth (John Leguizamo) and Diego the saber-tooth (Denis Leary) were escaping from encroaching glaciers. (And in the case of the first two, at least initially, trying to return a human infant to the hunter-gatherer tribe who evidently killed Manny's mate and child for food. Morose as he is, mammoth Manny is big-hearted in more ways than one.)

Now they're ensconced in a happy valley where young mammals water-slide through ice formations in a veritable Pleistocene Park, but the weather report predicts a change. The glaciers that surround them are rapidly melting, and with no way out of the valley, the animals must trek to a supposed boat in which they can ride out the storm. (No, there's no Noah.) That the warning and the direction to supposed salvation come from vultures who presumably prefer dead meat (and can fly outside the valley to look for more when the supply here runs out) is only the first bit of internal illogic that makes this often fun and funny feature a good film but not a great one.

The original Ice Age (2002) was about the value and strength of family-both biological and, in the blended-mammal "herd" of Manny, Sid and eventually Diego, surrogate. It's hard to imagine how this message of tolerance and celebrating differences made the first film a relative hit in these not-so-United States-and I've absolutely no idea how diehard conservative parents explained the clearly gay rhinos to kids without choking on their bile.

The sequel doesn't really have a theme, unfortunately. Manny, believing he's the last mammoth, does accept the imperative to reproduce with Ellie (voice of Queen Latifah), a female he finds-and who, in a cleverly sustained but knows-when-to-quit comic conceit, believes she's a prehistoric opossum, having been raised by a family of such and now imagining herself the sister of the teenage-boy-like Crash (Seann William Scott) and Eddie (Josh Peck). Once again, it takes a certain delicacy to explain to the child-centric audience that, "Well, kids, Ellie gets insulted by Manny because she thinks he wants to have sex on the first date! Silly mammoth...doesn't he know you wait for the third?" Basically, sexual misunderstanding is the big plot point driving a wedge between the two mammoths and their respective opossums and posse. Kids might be advised to brush up on their Doris Day-Rock Hudson movies first.

Whatever the story's about-other than the obligatory sticking-together-to-fight-adversity thing and the never-give-up-hope thing (they must've forgotten the follow-your-dream and need-to-redeem-oneself things)-I'm not sure the filmmakers could say. Fortunately, this CGI movie abounds in well-paced gags, both visual and verbal, occasionally punctuated by semi-connected silent skits featuring the unnamed-in-the-film squirrel/rat Scrat, whose dogged pursuit of an acorn is part Job, part Wile E. Coyote. There's also an unexpected, Busby Berkeley-styled musical number that, in retrospect, is probably exactly what buzzards would sing.

Diego remains an underwritten character-and I can't believe I'm saying that about an animated cat, especially one who calls himself a saber-tooth tiger even though none of the saber-tooth cats were tigers! Diego doesn't even have stripes, for goodness' sake. That Ross-from-"Friends"-like criticism aside, the movie looks gorgeous, it only lags a little here and there, and it growls with two beautifully icky (or should we say "ichy") sea-monster menaces who do off a minor supporting character who's not an extra. Combined with the prickly-real friendships among the leads, it makes me want to see another sequel. In three or four years.

-Frank Lovece