The worst part of it IMO is that Adventure 2 arguably set a barometer for how levels for virtually all Sonic games would be built going forward. This is especially obvious when comparing the (fairly accurate) level map guides for the stages from Prima Games. Adventure 2 by comparison feels like each stage was built off of an underlying template that it refuses to truly break away from. Adventure 1 wasn't perfect by any means but it still had a solid range in the way the levels are designed that each stage offered a distinct experience whether it's in the setpieces/platforming challenges, level mechanics, the enemies, or just the actual geometry/construction of the levels themselves.

The thing that really cements Adventure 2 as the worse entry of the two (and why I generally dislike Adventure 2 as a game overall) is how the level design is for me a drastic nosedive. Sloppier controls and slower movement with longer levels for the former, and a gimped radar that makes emerald shards harder to find with stages twice/thrice the size for the latter. And those branches into different genres kept from Adventure 1 (mech-shooting and emerald hunting) I find far less tolerable in Adventure 2. as out of place and awful Big's fishing levels are, he's only four levels to Sonic's ten) Adventure 2 ropes everybody into two campaigns, genre roulette and all, and there's a more even distribution of levels per character (everyone on average has about four-five).

Whereas in Adventure 1 everyone had their own campaign for their gameplay and in terms of content, Sonic with his Sonic gameplay had the biggest slice of the pie (i.e. Adventure 2 is more technically polished but the underlying game design is streamlined and/or refocused in the worst of ways.

Sonic adventure 2 dreamcast mod