K-ON! has been at the forefront of what's popular so far this anime season--developed by anime production leader KyoAni (which brought you Haruhi, Lucky Star, Clannad), K-ON! tells the adventures of four high school girls that desire to start a band together. Imagine Lucky Star without the otaku references and instead, with music.
The characters are your stereotypical anime archtypes. Yui, the dreamy, distant type who just screams MOE any chance she can get. Then there's Mio who's your typical tsundere character: seems to be hard and stern at one moment, and the next she's blushing and being cute. Ritsu, the leader of the club, is slightly spastic and hyperactive all the time--she actually bounces off of Yui and Mio really well. Then finally we have Tsumugi, who provides food for the club and for fans of Lucky Star--you will instantly be reminded of Miyuki.
Overall, it has it's few hilarious moments, but it isn't that great so far. The animation I have felt isn't up to KyoAni's usual standards--hands have bothered me so many time within the first three episodes. Humorous moments, while offbeat, still doesn't feel like it has that Lucky Star vibe (though Lucky Star didn't really pick up until later on in the season). But when K-ON is funny, it really is funny. The characters are memorable--Yui and Mio, fan favorites, are going to be the stuff of KyoAni animation legend once the series is through.
However--where it really shines is, in my opinion, is the OP (Cagayake! Girls) and especially the ED (Don't Say Lazy). The ED is fully animated with movement, which you see very rarely in anime. The song, I think, is catchy and the animation for it is brilliant.
Overall, K-ON! is a good, solid anime--but I have found it, so far, not living up to it's typical Kyoani expectations.
Worth watching? Of course. It'e the anime of the season.