Having only Sonic playable certainly does away with the problem of cluttering things up with too many pointless playable characters, however, it also feels like a step back since when done right - like with Tails and Knuckles, the idea of multiple playable character can greatly enhance the game’s replay value and put some new spins on existing levels.The Sonic 4 name irks me a bit because of how many things have been removed from prior games.
Sonic 4’s first episode has you controlling Sonic through four stages with a three act structure, ala Sonic 1, each has a boss battle occurring right after the third act is saved, instead of happening right at the end of the level - presumably so top scores and ring counts on leaderboards could be an accurate representation for each act as opposed to dropping off dramatically due to a boss draining them. It’s technically very good in many ways, and features some new things compared to the ‘90s Genesis games, but not many, and the usage of classic level archetypes makes them feel recycled even if the level designs are largely new - and it doesn’t help that boss battles are recycled from past games - with some new attacks thrown in. After a 16-year absence, consoles finally have a new side-scrolling Sonic adventure, and it winds up being a strange marriage of something blue, a few things new, and many things borrowed.