I've been playing <3 all night. I have a million things to say about it, almost all of them good, but I really need to get some sleep right now. I will say this, though - the Zoo is just about the greatest level I've seen in a game. And its background music? A medley of every song from Katamari 1, sung by animals, with a different animal taking the lead for each song. Que Sera Sera's vocals are by a cow, for example. It RULES.
Unfortunately, other than that and one or two other choice tracks, the music just can't compare with the original's soundtrack. Don't get me wrong - it's better than 90% of other game music, but most of it lacks the brilliant infectious quality that the original music had. Most of the tracks that I've heard are much more subdued, in the same vein as the bossa nova track from the original game, rather than energetic, poppy, or catchy. And while I love the original theme (Katamari on the Rock), I believe I've counted 3 covers of it so far in <3. That's a bit excessive. The returning singers from the first game deliver only half-as-good tracks, too - the guy who sang the awesome ending theme from Katamari gets stuck singing an only 'pretty good' cover of Katamari on the Rock, and the rapper from Getsu to Oji's song isn't especially great, either. I hate to make this comparison - really - but it reminds me a bit of the Parappa the Rapper 2 situation. The songs would seem pretty awesome if the original game (and Um Jammer Lammy) hadn't set the bar so high, but since it did, they come across as only pretty-good.
That said, I still had a huge-ass grin on my face the entire time I was playing the game, so obviously they're still doing something right! Don't expect a mind-blowing, legendary soundtrack like the original - just a really solid, above-average one. And of course, there's still a lot of room for it to grow on me. I definitely found myself liking certain songs (particularly "Kurukuru Rock," which was downright obnoxious at first) a lot more as I had the chance to listen to them a few times through.