I think much of Todd VanDerWerff’s analysis of the similarities between Community and Glee in this piece is correct, particularly this:
On Community, the baseline reality of the show will change from episode to episode, with each new half-hour setting up a completely new set of circumstances for the characters to navigate through. In the second season, the basic premise of the show itself—a group of characters comes together at a community college—hasn’t always been the premise. Sometimes, they’re not at the college but in the desert. Sometimes, they’re fighting zombies. Sometimes, they’re animated. It’s been audacious, to be sure, but the series has managed to work its way through most of these episodes by keeping the characters mostly consistent. The level of detail work the writers have done on the characters is remarkable, meaning that Britta and Annie will react roughly similarly whether they’re taking a class on feminism or battling in an all-out paintball war. The circumstances of the show change; the characters do not.
The exact opposite is true on Glee. The writers of Glee will change the characters to suit whatever whims they have that week.
One thing he doesn’t mention that I think is a significant challenge for both shows is that they both run against a ticking time clock. In Glee, the main characters will graduate and go off to college at some point. Presumably, the characters in Community will finish their two-year Associations programs at Greendale and transfer to other schools to get their B.A.s, though Dan Harmon could decide to keep them there for a full four years. Either way, at some point, some of the characters have to move on.
I think Community is more vulnerable to this structural challenge than Glee is. Whatever else can be said about Ryan Murphy, his show has done a terrific job of introducing new characters and integrating them into the main cast. At the moment, it means Glee is in danger of cast overload. But in the long term, it means it will be much easier to phase characters out as they go off to college and to have replacements ready to step into the gaps that they leave. Does that mean the show can survive without Rachel, its crazed core? That question remains to be answered, but the experiment of sending Kurt off to another school has worked well, expanding the show’s universe.
Community‘s got much less flexibility built in. The show keeps introducing and building out new characters, but they remain largely at the periphery of the show. Chang isn’t even a full member of the study group, and he’s been a core secondary character for the entire two seasons. Dean Pelton’s a permanent part of the landscape, and would be an important part of the transition, but he’s an administrator, not a student. Starburns, Fat Neil, Rich, and Leonard are all fantastic parts of the scenery, but there’s no way to be able to tell if they’d be able to fill a full slot in the study group. I think it might actually be smart for Community to commit to four seasons, but be firm about ending the show after that run. The chemistry it’s created is so specific to the core cast that it would be too bad to see it falter.