That image right there is everything I hate about S3.
Season 3 is a pretty strong litmus test for how committed you are to the show.
Chaos Theory, Horror Fiction, Holiday Music, Lupine Urology, and Digital Estate Planning are pretty great episodes that were entertaining to casual fans.
The Dreamtorium and Chang Takeover bits require a much higher level of involvement.
That's a load of crap. It's not about the level of involvement or how committed you are, the show just flat out drifted off into lala land. Season 1 & 2 had a lot of quirkiness, but other than a few things here and there which pushed the boundaries (the Paintball episodes being the biggest ones), it was for the most part taking place in the closest thing TV has to reality. The characters felt as much like real people as you get in a TV series, Greendale, mostly, kinda, felt like a real place, at least in a TV adapted, maybe slightly unreliable narrator-esque way. And even when it did push the boundaries, the good writing and acting kept it grounded, because the show acknowledged the weirdness even as it went along with it, and because it always came back down to earth a bit.
IMO, the problem probably started with the Paintball episodes, and how popular they were. They took something that was awesome because it was different, because it contrasted with the normal mood of the show, and started making every episode and plotline in that manner. Like Cantatus said, they probably got comfortable, 'oh, the viewers like weird unrealistic fantasy scenarios and parodies that would never happen in the real world? We'll give them tons of it!' But those episodes were good because they were rare, they only worked as a contrast to the regular reality the rest of the episodes took place in, when they became the norm the show just completely diverted from that reality and became some kind of weird fantasy trip.
That said, despite not generally being a fan of how far out of reality the show went in S3, it wasn't all bad. Remedial Chaos Theory has already been mentioned, and I also liked the episode with Annie and Abed in the Dreamatorium. But even then, compare it to the Season 1 episode where Britta pays for Abed to start taking film classes. Both episodes are about Abed reflecting on his ability to relate to the people around him and the fears which stem from that (interestingly, the episode in S1 is about his fears about the past, and the S3 episode is about his fears of the future), but while the season 1 episode involves Abed using a handheld camera to film people as he wanders around campus, then cutting the clips together and editing them to play out and express his worries, Season 3 involves Abed and Annie running through some shared hallucinatory dreamland, jumping in and out of parodies and scenarios taken from other shows. Both deal with the same theme, but in wildly different ways which demonstrate how much the tone of the show had changed in S3.
If you want another example, look at the intro to the first episode of S2 & S3. S2 has the characters jumping out of bed, getting changed etc, in a montage with music played over the top, while S3 has an extended fantasy song and dance CGI sequence.
None of that crap is bad because it's complicated, or difficult to understand unless you're 'committed' enough, it's bad because it's a massive shift in the tone of the series which makes the characters and their experiences impossible to relate to. I can relate to and sympathize with Abed using his creativity to circumvent his inability to communicate with the people around him and expressing his feelings about his family to his father through a video clip which he's put together, much, much more than I can understand or relate to him making an emotional breakthrough because he spent an afternoon playing make believe hopping through shared imaginary dreamscape TV show parodies. Everything that happened in that S1 episode could have happened to a real person, in real life. The S3 episode? Not so much.