I can't say as I found this episode to be very funny. Usually there's one or two jokes that will stick with me after watching an episode, and nothing really stands out this week. It seems like the writers were relying too much on the origin concept to deliver the jokes while the origin concept was too busy trying to piece together a cohesive story.
Though, as far as concept episodes go, I do think this is one of the best this season. This isn't the first show to attempt an origin episode like this, and I think the Community writers were able to deliver on it while remaining faithful to the characters and not having to strain what we know about them too much. They also stayed away from the temptation other shows have gone with of going really over the top with the flashbacks. Despite not really delivering on the jokes, I think this (and all the fan service) made it what would've been a much better way of opening the season rather than that mediocre sitcom one.
However, I sort of wish they went the opposite way with the conclusion of the episode. While I appreciate that the writers were able to come up with a credible explanation to connect all the characters before Greendale without conflicting with what we've learned over the previous seasons (though, I have read there were a couple minor retcon errors), I can't help but feel the idea that they were all "fated" to form the study group undermines one of the central themes of the show: that these were all people who have next to nothing in common that have formed a sort of de facto family. Too often this season they've gone with the happy, easy ending (generally in the form of a Jeff hammering us over the head with it in a monologue). I think this episode would've worked much better had Abed's ideas not panned out and left us with the not-so-obvious takeaway thatthatis what makes the group even more special, though I think that would require a certain level of subtly the new writers really haven't shown.