Weird to say since this was a smash hit game, a system seller that put Sega on the path to market dominance for a generation, but most people these days seem to say that Sonic 1 is much less fun than later entries, and I have to agree. It's hard to recommend this to people, but it's much easier to recommend Sonic 2, Sonic 3D, Sonic 3 & Knuckles, Sonic Adventure, Sonic Adventure 2, Sonic Mania, and basically any of the Boost games since they're all casual shit in the first place . I'm a big fan, and my friends see how much I like it, so they try the first game, and it never hooks them. Sometimes I tell them just to skip to one of the games I just mentioned, depending on what types of games they like, and they usually enjoy whichever one I recommend. But the first game never hooks anybody I can find these days. And I seem to hear similar thoughts from everyone on the internet.
Some people say it's because the first game has more slow sections, notably in the second zone, so very early in the game. I suppose. The level design just isn't quite as much fun. While you can speed through most levels when you're good at the game, it still doesn't feel as fun as the later games. Plus Labyrinth Zone sucks balls compared to all later water levels. And Spring Yard Zone, while clearly a spiritual predecessor to things like Casino Night Zone, obviously lacks the appeal of later Casino/Carnival/etc. stages. The Special Stages are much less fun than later games, too.
Also, I think the game is also just harder, and that turns off modern audiences. But I also think modern audiences are bitches, and Sonic isn't terribly hard for a game from 1991. Harder than Mario World, I suppose, but it's still nothing crazy. Sonic 1 and 2 also lack save functions, and modern audiences tend to hate that, but for some reason the people I get to try the series never have as much of a problem with that in Sonic 2. I have to chalk it up to either Sonic 2 being easier, at least until you get closer to the end. At least if you run out of Continues at Metropolis Zone you feel like you experienced a lot already, you had a lot of fun with the game. I'm willing to bet most new players, at least these days, don't make it past Labyrinth Zone. And I suppose even if they do, and then they die at Star Light Zone or something, you might have a bit of a bad taste in your mouth from Labyrinth.
And oh yeah, making you go back for a fourth act of Labyrinth Zone right at the end of the game sucks. Fuck Labyrinth Zone. It's not the only reason Sonic 1 pales in comparison to the later games, but I keep finding that many of my complaints relate to it.