The first part of this game (up to the Master Sword and the first Agahnim fight) was 10/10 for me, giving you clues about where to go next but never holding your hand too much, letting you explore freely to find some secrets with the items you've obtained up to that point. The remaining 2/3 of the game were overall a bit more confusing about what to do between one dungeon and another, and I had to check a guide to find some useful items in the overworld (I recommend going for 100% items and heart pieces, because in this game you take A LOT of damage in some parts, especially in the Dark World) as some stuff wasn't that clear, but apart from that every dungeon was well designed and the game in general, although pretty tough, was never unfair. I understand why it is considered a classic.

I decided to replay this game after playing through all of the four main classic Sonic games, just for fun. I expected a really bad experience, but... I kinda liked it?
I think the main reason people complain about this game is because of its title, and I think it is legit. If you play a game called "Sonic 4" you naturally expect something that feels like the classics gameplay-wise, so I understand the criticisms on the game engine and the weird physics, but personally I never found any situation in the game that demands momentum-based action. If you see the levels as some automated, almost endless runner-like obstacle courses (and I think it makes sense, since this was originally planned to be a mobile game, before being rebranded for nostalgia's sake) maybe you would enjoy this game a little more, but don't get your expectations too high, of course.