I've gotta be clear on this, though. I'm not defending Sonic '06. I've disagreed with Cube many times about this, lol, but Sonic '06 had absolutely shit level designs. In almost every sense of the word.
That said, once you commit to memory levels like Kingdom Valley, Flame Core, Dusty Desert, and Tropical Jungle, you can go through them pretty quickly and actually have some fun. Some fun. There's some great music in there and the visuals have a very Sonic Adventure-like art design.
Sonic and the Black Knight just doesn't allow for any fun. Levels are all very short, have no speed, and are pretty much impossible to enjoy. I found almost nothing redeemable about the game whatsoever.