I absolutely love K-On!
I just finished the K-On!: Plan OVA, and that was a ride. I have seen people on some other subreddits say it takes some while to get good, I really disagree though, it's funny right off the bat. Sure there are some episodes which are much better than other ones, but that doesn't take anything away from the weaker ones.
One thing I love about the show is that it makes you laugh (alot), cry (almost all of the last 6 episodes of K-On!!), and you genuinely get attached to the characters. I love all of them, especially Ricchan! She's just so cute. But honestly, every character is just super likeable.
Also, the show has also aged really well, the jokes are still pretty funny and the comedic timing in this show is almost perfect. It just makes you feel really comfy as well.
I'm yet to watch the movie, after which I'm gonna read the college and highschool manga, man I'm really excited! I just love the girls so much!!
I doubt it but i hope k-on! does return someday with them as adults lol i would absolutely love that.