I believe the only way to enjoy K-On! is to accept the essence of a "slice of life" anime at its fullest. Far from being the downfall of the genre, I believe that this anime truly reflects what SOL should be: a brief glimpse into the lives of a few individuals which gives us a chance to empathize with them and enjoy their daily shenanigans. The girls in this show are not the absurdly complex characters with dark pasts you expect to find in other anime, but that's what makes K-On! such a treat. Passing the time from episode to episode you find yourself growing to love the protagonists for what they are, just a couple of girls in high school trying to have some fun and play great music.
On that note, this show is utterly hilarious. A majority of its content relies not on story arcs, but rather on moment-to-moment comedy and bits. Furthermore, the musical references K-On! makes are excellent and the songs the girls play are more than catchy. You'll find yourself becoming drawn in bit by bit, until you eventually realize that while not much has happened you still don't want it to end.
I believe K-On! understands exactly what role it plays, and delivers adorably wonderful humor in what was one of my favorite anime.
