Not as bad as I recall, honestly.
The thing with Sonic as a franchise is that it's sold as "BE VERY QUICK DO FAST STUFF SPEED UP ETC" but if you take your time during the stages and explore, there's actually a very fun platforming game behind it. Hell, I even took my own time with the special stages and they didn't feel so jarring this time around.
However... as much as I'll credit these points to the game, it's still somewhat too early on for the franchise, so some enemies are a bit of a slog to deal with, the level design has some rough moments (Labyrinth and Scrap Brain act 3, specially), and I have a severe distate for the amount of bottomless pits in this...
Still, this game does share some nitpicks I have with the first Mega Man game, that thankfully were adressed and improved upon on the following games (specially Sonic CD!)
Not the greatest start to one of my favorite franchises ever... but still, it's only upwards from here on the Mega Drive era!

I feel like an outlier when I say I really love this game. Compared to all of the other classic games, I find myself revisiting this one the most and enjoying each playthrough I have of it. I never grew up with this game, and I only beat it during my time in middle school. I still love replaying and beating this game in one sitting to this day. There's not a lot to this game, but there's a lot to love. It's a stellar and unique art direction, paired with the amazing music from Masato Nakamura. It all adds to the unique style Sonic was exuding back in the 90s. I have the Special Stage music from this game as my ringtone because I love it that much.

A lot of people tend to have this misconception that Sonic has and always will have the gameplay mentality of "going fast" and critique this game based on that misconception. I think that Sonic, from a design standpoint, has always encouraged players to properly learn the level design throughout the game and earn the satisfaction of beating a level quickly through skill and memorization. I feel like people give too much hate to Marble Zone and Labyrinth Zone because they refuse to engage with the level design and just want to hold right the whole time, like they can do in Green Hill. People forget that Sonic has always had level design that rewards exploration, and there are routes and gameplay tricks you can use to skip entire sections of levels. Scrap Brain Zone Act 3 has a shortcut that cuts the time from 2 minutes to 20 seconds. I don't think there's anything wrong with slowly but surely making your way through a level. At maximum, levels can take about 2 and a half minutes to complete with plenty of mistakes, and people overblow how long these levels actually are. I'm not going to act like the game is perfect; some of the enemy placement and level design in Labyrinth Zone and Starlight Zone are pretty annoying, and Scrap Brain can get tiring. It's got first-game syndrome, sure, but it isn't terrible. It can be pretty frustrating on first playthroughs, but I feel like that's everyone's first experience playing a Sonic game. It's a rite of passage at this point. 

In retrospect, this game can seem pretty terrible, but I have my own fun with it. I wish people shared the same sentiment. Special stages are bad, though I won't deny it; I've just gotten used to them over time.

Esse jogo me gerou muitos sentimentos. A maioria deles se derivava do ódio imensurável que eu sinto por grande parte desse jogo. Uma primeira fase que, uau, esbanja criatividade e diversão, apesar de ter achado ela "complicada" de se jogar em alta velocidade na primeira jogatina.

De resto, é só tristeza. Tem uma ou outra zona(como a Spring Yard Zone) que é até satisfatório de jogar em certos pontos... só em certoooos pontos.

A trilha é sonora é meio a meio pra mim. Em parte eu gosto, mas em parte eu não ligo muito. É um efeito engraçado.

AMO o design da fase da Green Hills Zone, assim como o design do ouriço mais veloz de todos. Acho que até o design de personagem do grande vilão cabeça de ovo me pega muito nesse jogo. De resto eu não tenho o mesmo apreço, apesar de não chegar a odiar... exceto a Marble Zone, essa eu odeio muito.

E não, eu não irei pegar as esmeraldas do caos pra ver o final verdadeiro. Eggman, eu espero que um dia mijem na sua esposa.

Dito isso, um jogo quase que tenebroso. Quase.

(Sim, eu sei que eu fiz a resenha no jogo errado, mas agora tá certo)

The proof of concept game.

Platforming here is excellent and there are some especially tricky and difficult parts. It takes a minute to get how the momentum works but once you get it down it feels really good to play. Of course the music is quite good and even though it's an early Genesis title there's some excellent music here.

The only downside of this game is that the levels are a little too long. This game makes you really grateful that they dropped the 3 act structure in Sonic 2. There's a lot of set pieces that are copy/pasted into the level at random so at times it feels like you've somehow looped back around.

Sonic é minha franquia favorita, e provavelmente o personagem mais importante da minha vida. Sonic 1 tem o peso da nostalgia, e pra sua época era ótimo. Mas, não envelheceu bem. O principal erro de Sonic 1 é o level design, que não valoriza o que há de mais importante e diferente na franquia: a velocidade. A green hill é a única zona que explora isso bem, por isso se tornou a fase mais memorável, mas dali pra frente, vira um jogo de plataforma comum e até traiçoeiro. Dito isso, os gráficos são belos, as músicas ótimas e tem muita identidade. É ok, mas agrega valor por ter sido o ponta pé inicial para nascer uma das séries de jogos mais iconicas e relevantes de todas!