Story: K-On! is simply about high girls starting up a music club and getting the chance to have fun playing music together and whatnot. There really is not much plot outside but somehow the anime works. The events that they go through are not particularly unique nor are they extremely dramatic. Instead, they are light, entertaining, and rarely boring. So despite having a non-spectacular plot, I kept wanting to watch episode after episode. Since the series runs for about 13 episodes, everything was consistently entertaining (and very endearing) and nothing was ever dragged out.
Animation: Bright and bold but slightly toned down for the most part, matching up with the atmosphere for K-On! The character designs were fairly distinct and the background was not forgotten. Animation of motion and of the playing was done pretty nicely as well. The animation was nothing spectacular but then again it was still pleasing to the eye. On occasion, the animation could be slightly sloppy and unclean but on the whole, it was fairly nice.
Sound: Probably my favorite part of the series. The catchy opening and endings were definitely fun to listen to and sing along with and the tracks that the bands played were all enjoyable. The soundtrack was sweet and cute and added personality to the series. The VA's did a great job with their characters. No one had an annoying voice. They all sounded matched up with their personalities while sound like the high schoolers that they are. Nothing bad to say about sound.
Characters: Most of the characters fell under stereotypes but in this case, that was not such a bad thing. They were all likable, slightly unpredictable and had some slight quirk that added a little personality to each character. Every episode, most of the characters were teased for their stereotypes but the jokes stayed fresh and never got too old. Most of the characters stayed the same but some grew slightly. The most important part for the characters were the interactions and they fact that they grew to be like family, having fun together and doing what they loved.
Overall: Though the anime was nothing significantly unique and mind-blowing, it was genuinely fun and sweet entertainment. This would be good for anyone who likes slice-of-life, watching school kids enjoy life, or simply watching a sweet wholesome anime that requires little thinking but has good music and an endearing plot.