Sonic is one of those titles that you are either a fan or not. There is not a lot of wiggle room for anything in between. Gamers either love the high speed gameplay or they loathe it. Going by sales, and sequels to capitalize on those sales, it is safe to say there are a lot of fans out there.
Sega took a lot of chances with their consoles, Sonic and Knuckles being one of them. Before this title, there was no real “add-on” option for cartridge based titles. Sure there was the Game Genie which used similar technology, that was not an add-on option, it did not add anything new to the titles attached to it. Sonic and Knuckles does.
The main draw for this title was that it offered up a new character, Knuckles, for players to enjoy familiar territory with. We did not see this type of technology again in gaming, probably because it is harder than it looks to create interlockable games. There were rumors when Street Fighter II hit the Super Nintendo that it would use something similar to the Sonic and Knuckles method to update the game with access to the boss characters as player controllable but that obviously never panned out.