I think some of the reasons Community has such a fervent fanbase are due to it's more unfortunate qualities, like being so obsessed with media trivia that it's got two whole characters who are 80% trivia, and doing creepy things like that episode where Allison Brie sang in a baby voice about wanting Jeff to be her daddy (who she is in love with on the show), and the intention that this was to be a sexy and cool thing (they constantly do this with the character of Annie, who is a Sexy Schoolgirl)
There are other shows which, although they've also got some problems with their comedy ethics!!!! are still so distinctive that I totally understand why people go nuts over them, like Arrested Development and stuff like that. I don't really see this in Community where the comedy seems to be a mix of, in order; average sitcom jokes, stuff that's meant to be funny because you recognize it, and meme-style non sequiturs like you used to see on Scrubs* (Pop-pop! Starburns!) (Actually, this kind of stuff doesn't usually bother me, I like nonsense, but amidst the derivative writing and gross nerd shit that dominates the rest of the show, them throwing in these kind of easy laughs doesn't work for me)
I guess another part of the appeal, which isn't necessarily a comedic aspect, but attracts nerds, is the high-concept episodes they tend to do. I don't have any problem with that at all in theory, but it feels like it's just something they do which doesn't necessarily heighten the quality of the episodes beyond on a nerd level - although on the nerd level, there is also the fact that most of these high-concepts are riiiiifffffs on common genres/tropes (they did a zombie apocalypse episode, and a paintball episode that just riiiiiiifffffed the shit outta everything. So god damned aware of other things people did, these guys are.). It's a very easy thing to do, and creates a pretty convincing illusion that the show is wacky and crazy, but it's often done for no other reason than to do it and doesn't actually provide any space for jokes or storylines they couldn't have done anyway. So maybe nobody gives a crap about that, and doesn't need to think about how their comedy shows are structured that much, but if you do, the gist is that Community does superficially exciting things that don't really go anywhere and might not surprise or excite you all that much after all.
I've seen all of it, because I'm just one of those motherfuckers who finds huge amount of TV really easy to watch and when I find a show I can stand, or find interesting in one or another way (not necessarily liking it or anything), I tend to blow through most of it in a few days. Community is a show I am always on the verge of turning off and I have in irritation then gone back to at a moment of boredom while sitting in the office at work or something. It takes a lot for me to drop a show because I'm one of those god damned people, but if you aren't then there are better comedy shows out there to watch. Not many, but Community is something I think is actively gross and I'm a little pissed off at myself for having watched so much of it. Maybe I will drop it after all. Britta is pretty funny in season 3 though.
*Community is comparable to Scrubs in a whole bunch of ways, but I'd say Community is less objectionable than Scrubs because Scrubs was flat out bogus especially on gender and using lazy comedy stereotypes. Also it stars that fucker Zach Braff, who I think in my head has murdering-parties with Jack Black, Vince Vaughn and a bunch of other fuckers. He's literally a serial killer of women, in my brain.