If you're up on the Dan Harmon vs. Chevy Chase blood feud, I have to say I agree with Chevy on two points:
1) They've really run out of anything remotely funny or interesting to do with Pierce. Since they retreated from the ledge of making him full-on-evil (which resulted in probably the best work Chevy has ever done anywhere in the D&D and bequeathal episodes) he's basically been doddering around on the margins. (The best example is last night and I think if he stays we're going to see a lot more Pierce-Chang pairings, to the show's detriment). I won't be surprised or sorry if the show comes back in the fall without Pierce in it.
2) The post-hiatus episodes are still entertaining and hang together well as a show, in terms of storyline, character development etc. it's as good as ever. But they haven't been very funny, for the most part. For instance the only things I laughed at in the Ken Burns ep were the campus map gag and Britta's photography. Everything else was engaging, well crafted and performed, but far from hilarious. I'm not sure that's something they absolutely have to correct - if the characters and story are working the laughs will come, most of the time - but I can see why a guy like Chevy Chase who gives every indication of being as shallow and slapsticky as his character would think fewer jokes landing mean the show has turned into a "mediocre sitcom".
I think the post-hiatus episodes have been better than the pre-hiatus episodes. The Dreamatorium episode and the Law and Order episode pushed it ahead (and I recognize that they hadn't yet aired when you made this post). Of course, the first half had the classic that is Remedial Chaos Theory but this half has been more consistently great.