Sonic the Hedgehog (the game, not necessarily the character) feels like a lost relic from the past.

Sonic games are known for their blistering speed but Sonic 1 only allows players to experience high-speed gameplay in bitesize chunks, sandwiched between slower zones that require more precision platforming and patience. It's an approach later Sonic games would stray away from.

I've played the likes of Marble Zone and Labyrinth Zone enough to have a soft spot for them but I can empathise with younger fans who might visit this first instalment and wonder what all the initial hype was about (this game was, after all, highly acclaimed on release).

Even if we admit that the Sonic formula needed a little refining, this is still a brilliant starting point. Sonic controls so smoothly, the kooky graphics paint a world that's fun to explore and the soundtrack is one of the Mega Drive's best. There's so much to appreciate here if you don't get hung up on the game's slower moments.

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.

The first 2D Sonic game I beat (I used save states). I played this on the "Sonic's Ultimate Genesis Collection" on PS3 just in case it isn't a faithful experience to the original.

It seems like the kind of game I would've probably loved as a kid when new games were few and far between, so I played the same game for months. I played for a casual game to beat, rather than a game where I really wanted to learn the levels to find optimal routes, so that probably lessened my experience a bit. The big levels are cool conceptually because you can explore and have different experiences each time you play, but I prefer more linear levels. Sonic did not feel good to control, he felt slow and clunky. He's surprisingly very vulnerable because he only has hit boxes when he jumps, so that means when he's running, falling, or jumping on a spring he's vulnerable. I wasn't a fan of the enemy designs, I don't think they did a good job at illustrating if and where you are able to damage them. I struggled going through what seemed like scripted sequences like running through loops and jumping off of slides. There were times where I ran faster while I wasn't touching the controller, which was odd to me. Collecting the Chaos Emeralds felt like a slap in the face. The bonus levels are so hard, I still don't understand how the rotating works. In the end, your reward for collecting all of the emeralds is an ending that is extremely similar to the normal ending. For a character that is known for his speed, Sonic doesn't have a lot of options to build up speed in this game.

Even though I didn't like the game, I'm still glad I finished it. I am still looking forward to the later games because I think they will at least address some of the issues I had with this one.

Edit: I forgot to mention that there were odd performance issues where the game was chugging at points. And I usually don't mind underwater levels, but they're atrocious in this game. I think it's because you can't stay underwater indefinitely like you can in Mario. It didn't help that the big air bubbles seem to spawn at random intervals even while you're waiting at their spawn points. Also, these levels were not very memorable. I literally thought I must have failed at one point because the level I was playing was so similar to the level I had just beaten.

Edit 2: The invincibility frames are way too short. Way too easy to get hit with a 1-2 and lose. This issue is even worse when you consider how hard it is to recover your rings.

Sonic the hedgehog is a game that was truly ahead of its time. The music in sonic 1 is so iconic, whenever you hear it you know what game it's from. The same can be said for the sound effects, whether it's collecting rings, finishing a level, or almost drowning. Each sound is truly iconic and special in its own way.

Another thing about sonic 1 that's amazing is the level design. The levels are full of spaces to explore and different routes to take. It really does baffle me how on Sega's first try they managed to get everything so right.