Sonic 1: OK, Marble and Labyrinth zone get kinda tedious
Sonic 2: Awesome but the level progression feels random & special stages are hard as shit
Sonic CD: Complex level design that encourages exploration a little confusing at times, creative but kinda easy boss battles, Awesome music, Cute cutscenes, Good game
Sonic 3 & Knuckles: A huge adventure with all 3 characters with a minimal plot and sane progression in many diverse level, great level design, memorable music, Greatest game
Knuckles Chaotix: Rubber band mechanic unnecessarily complicates controls, bland basic level design, chaotic special stages, cool looking bosses, some interesting ideas but boring overall
Sonic Spinball: Western style Sonic, pinball action with small control over Sonic. Some animations are cute. RIP headphone users. Okay I suppose if you're into pinball and Pingas Robotnik memes. The 8bit version is one of my painful guilty pleasures although it runs in like 9 FPS
Sonic 3D Blast: Boring fetchquest in each level, speed is not earned, ugly plastic prerendered graphics, boring
Sonic 3D Blast (Saturn): Same as above but with awesome looking 3D Special Stages
Sonic the Fighters: Fun fighting game with Sonic characters. The squish and cartoony effects are cute. Bring back Rocket Metal.
Sonic X-treme: Overrated cancelled 3D fisheye looking Sonic game.
Sonic R: Promising Sonic foot race game that really needed many more levels, powerups and better racetrack design. Another guilty pleasure.
Sonic Adventure: Interesting story progression, Horrible collisions, slightly slippery controls. Variety of gameplay styles ruins it (especially Big's fishing), okay game
Sonic Adventure 2: Trying too-hard to be serious/edgy plothole-filled story. Gem Hunting can get boring and frustrating. Jiggly bat tits.
Sonic Shuffle: The boards are not very interesting but some mini games are kinda cute. The music gets from funky to weird. Many say it's a Mario party ripoff. To quote Eggman "AWWWW YEAHHH??"