Thundercats 2011. The pilot episodes went far beyond my expectations. They've had great designs, decent action, a whole world to play with, interesting dynamics between the leads right off the bat...
And it never reached this level again. The third episode was utterly shit, felt like a slap in the face, really. Then they've spent the entire first half of the show continously rewriting Lion-O's and Tygra's characterizations. Once that settled, we've got bipolar Pumyra. And then the show ended, leaving me perplexed as to what the fuck did I even watch.
The showrunners talking about the stuff they had planned in case they weren't cancelled honestly just make me wonder, if they've ever grasped what they wanted TC to be about.