Mario's original "rival," Sega's mascot's first game is often seen as one of the most significant titles of the 16-bit era, as it helped push the "platformer with an animal as the star" type of thing that we still see today, and it's still heralded as one of the best games of all time. While it's not one of my personal favorites, I certainly see the significance of the game and I do agree, it's a really enjoyable title.
"Sonic the Hedgehog" helped push 2D platforming even further back in the day, as it took the idea of a straightforward 2D side-scroller and turned that around, giving us a platformer with more freedom of exploration, thus giving us more than one way to get from point A to point B. Throw in some incredibly lush, detailed environments and a character that runs at the speed of light and you've got a fun, fresh platformer that holds up to this day! The game is still fast, the controls still feel great, the graphics, even after over 20 years, still look magnificent, and the music is fantastically memorable.
The game does have a few minor flaws, however, that come from the age. Sonic's limited form of combat (he only has a homing attack) makes enemies kind of cumbersome to deal with, the overwhelming difficulty can be a back-breaker to some, and for a game where the point is to go fast, it sometimes feels like it's a bit better to move at a slower, more careful pace. Maybe that's just me, but sometimes, running too fast could too easily lead to death, which doesn't help matters when, again, the difficulty spikes are real.
All that said, I greatly enjoyed "Sonic the Hedgehog," and even after 26 years, this game is still a blast to play. If you haven't played this classic...well, 1. you haven't lived, 2. you're probably too young and your parents didn't teach you enough about video games, and 3. you need to fix that.
Final rating: 8 out of 10 "Great"