I see this is quite a polarising piece of content - as most 3D Sonic adventures tend to become. But for me personally, it may not be perfect, but it is a spectacular showpiece. Essentially a rewriting of the original game's final act, it certainly amplifies the challenge - quite substantially in fact. The design philosophy seems to have taken a catering to how players can manipulate mechanics for insane movement and it's an interesting philosophy that does hit the right spot in places. But it has a few potentially roadblocky moments with that difficulty spike, plus there are certain character moves that needed fine tuning to be more comfortable using. With perseverance however (and the odd switch to Easy mode, PLEASE don't feel ashamed in doing so if you want to pass a challenge), the climax serves up so much to get excited over as well as cheeky nods to other Sonic media for those who can recognise them.
My biggest win however is well over 15 hours extra playtime for absolutely FREE. That alone makes this DLC a winner and for how it made me hoot, holler and smile until my cheeks hurt in the big finale, this DLC deserves plenty of plaudits.