As if it's not bad enough that most of these USA CG animations are overflowing with cheap pop music, Alvin adds insult to injury by having the songs performed by a bunch of actual chipmunks. Even worse, that's apparently the whole selling point of this movie. Best viewed with the volume all the way down in other words.
The plot is extremely trivial. Three talking chipmunks end up in some annoying guy's home. He turns out to be down on his last luck as a music writer, but lo and behold, the chipmunks can sing, and they become an overnight sensation. There's also a romantic subplot and an evil studio mogul, but who cares really.
The blend between the CG and live action footage is pretty decent, that's about the only good thing I can say about this film. The acting is terrible, the comedy is bland, the music simply deafening. But it's a successful film that spawned a bunch of sequels and spin-offs, so I guess there's an audience out there that digs these kinds of films.