I don't give long reviews, so just read this and be done with it quick.
K-on is one of my favorite animes because of its cute story and fun characters. When I say story, it doesn't really have one. Just random events that somehow relate. At least I didn't feel stupid watching the plot (As with some other slice-of-life animes) Of course, the anime is about music, so obviously the music is top notch and the seiyuus do a excellent job at bringing the characters to life. We've got Yui the air head, Mugi the rich girl, Mio the hot babe, Azunyan the Saimoe champion 2010, and Ritsu the asshole (Jk). Since the animation is made by Kyoto Animations, we could definitely expect detailed animations (Yes, horrible wording XP).
Overall, I recommend this to those who enjoy slice-of life animes with basically no plot. Don't be gay by judging this anime by its cover. I'm a dude and I fell for this anime immediately (my friends all said it's too "girly").