With a series like K-on!, there is an over arching story, but the focus is more on the individual episodes, which I really enjoyed. There was some pretty good humor too and the adventures of the light music club were really great. K-on! kind of reminded me of Lucky Star in some ways, with its episodic feel and its light, humorous tone to it. One thing that I didn't like was sometimes when there was an episode that felt a little too simular to another one in the series, mostly the 2 episodes where they went away to a beach resort in the summer, but other than that it was pretty good.
The art and animation of K-on! is magnificent. The characters had a nice cute feel to it that can be found in other animes like So-Ra-No-Wo-To and Lucky Star. I felt that the animation was superb also and the performance sequences were done nicely.
I normally do not rate anime on sound or even mention it, but with K-on! being a music oriented anime, I could not avoid talking about it. I felt that the music that the band preformed was very good and pleasant to the ears. I also liked how in the dubbed version, they kept the Japanese version of the music.
The characters really make this anime shine. I loved all of them and they were each funny. Kio and Ritsu make a wonderful comedic duo, and they complement each other and lead to funny situations. Tsumugi is a very cute and entertaining character, and she reminded me a little of Miyuki from Lucky Star. Yui is just a fun character to watch as she is your everyday ditz. Her presence is very entertaining and is a really cute character. Asuza is also a fun character where she is trying to understand the rest of the band at the begining, and being an important part of it later on.
K-on! is a funny anime that should be enjoyed. This most definately has rewatch value and I recommend it highly.