The character stuff was OK. Pharma and Tyrest were cool, and he made a bunch of nobodies like Swerve into interesting characters.
But yeah, bearing in mind that I quit IDW after Dark Cybertron, when I think back I can't think of any topic he added to the lore that I like. His rewrite of the Cybertronian origin story was fucked up, Functionalism has a bunch of weird holes in it, and the stuff about spark mining/hotspots/cold constructed Cybertronians having their sparks torn out of the Matrix and all being evil just doesn't feel right.
Well, I take that back. The Shadowplay stuff is interesting. But everything else that he's done that was actually good has been more "events" than worldbuilding. I just don't think he's a good worldbuilder, or at least not a suitable one for this franchise.