Okay, let me tell you people something -
I practically hated an entire genre because of K-On! for two years or so.
I'm not kidding. The first "slice of life" anime that I ever saw was K-On! It was being marketed as a "sensation" and had advertisements where the girls were constantly singing and looking pretty while doing so. The animation looked shiny. I liked that.
Then I saw the episodes. And all I saw was Yui being clumsy and laughing and the girls eating cake and drinking tea (or coffee whatevs). There was no music, or, at least, not as much as I'd have liked based on the advertisements. Okay, I accept, the advertisements for the show are to blame and not the show itself since my expectations were distorted from the beginning. Yeah, fine, I accept that.
But it was all so pointless. So, so pointless. There was NO plot. Nothing. Granted, I saw like two episodes instead of watching 8-10 but I saw nothing in it apart from pretty girls eating cake and making merry - at that point of time, I used to watch anime to experience worlds. To experience tales of adventure, of romance, of action - anything. But there should be something. And K-On! lacked that something.
And I associated this lack of "something" with Slice of life shows in general. And for a good two years I avoided any show with a "slice of life" tag because I thought they'd all be pointless "no plot" shows like K-On! was.
Then I saw Clannad, Anohana, One Week Friends, Barakamon, Welcome to the NHK, Sakurasou no Pet na Kanojo, OregaIru, Hanasaku Iroha etc. And no, even though they all do belong under the same genre, they're not like K-On! in the sense that they possess a coherent plot. Everything that a character does in an episode carries some weight - their actions seem like they have some significance. Something, I'm afraid, I can't say for what I saw in K-On!
Don't get me wrong, I'm still open for giving K-On! another shot in the future sometime. But it definitely isn't fair to group it up with other slice of life anime imo because they do have something going for them while K-On! just comprises of girls being cute and making you feel warm and fuzzy inside (if you're into that kind of stuff). There's no "plot" - at least nothing I saw when I last watched it.
again, no offense to any K-On! fan over here. But these are just my thoughts on the show. and sorry for the tl;dr. XD;