Might as well post in this thread, more so after Polygon gave it a shout out XD.
Okay, Sonic 1 has issues and they are noticeable; the pacing between zones is a bit off (Speedy Zone then Slow One), the lack of a spindash could annoy people who jumped into the series with one of the later games and the level design while damn solid isn't as sharp compared to S2 or S3&K.
But for what is present, it is a very solid first shot at a Sonic game. The levels feel great to run through and if you know how to effectively use your rolling ability, it can make the game so much fun. Getting in a grove in Green Hill Zone or Starlight Zone is such a wonderful feeling. However, you have two very odd zones; Marble & Labyrinth.
That later is a big issue with Sonic 1 and is one of the worst zones in a Classic Sonic title, but Marble isn't that bad at all. It takes forever for your first run for sure, but the more you play it, the better it gets. Like the platforming it offers honestly

.
Sonic 1 has problems, but so does every first title in a series. Super Mario Brothers is a classic but it has some issues, Kirby Dreamland is great fun but it lacks Kirby's eating ability to get powers from foes, Kingdom Hearts 1 lacks the better camera that KH2 has, God of War 1 lacks the faster movement options when climbing that GOW2 offers.
Long story short; the first games have growing pains that get worked out in sequels. Sonic 1 is that case, with CD & Sonic 2 fixed issues that Sonic 1 had in many ways

.
People like to say Sonic sucks because his series is such an easy target thanks to painfully bad games like 06 and Boom Wii U being front and center when people think 'Sonic' sometimes. But the series has some bright points and some damn high points. So, judge the game on its own merits rather then the stigma that is linked to Sonic more or less OP.