Heavily inspired by ‪@larryinc64‬'s extended medley from August of 2015.
The video:    • Sonic Generations - Extended Medley (...  

Timestamps:
0:00 SEGA / Sonic Team Logo
0:09 Intro
0:23 Sonic the Hedgehog (Green Hill)
0:43 Sonic the Hedgehog 2 (Chemical Plant)
1:17 Sonic CD (Stardust Speedway JP)
1:46 Sonic the Hedgehog 3 (Angel Island, Smash Bros. Brawl Remix)
2:22 Sonic & Knuckles (Sky Sanctuary)
3:00 Sonic 3D Blast (Green Grove / The Air... for Windy Valley)
3:32 Sonic Adventure (Speed Highway)
4:13 Sonic Adventure 2 (City Escape)
5:21 Sonic Heroes (Seaside Hill)
6:15 Sonic Rush (Water Palace)
7:06 Sonic the Hedgehog 2006 (Crisis City)
7:56 Sonic and the Secret Rings (Evil Foundry)
8:51 Sonic Unleashed (Rooftop Run Day)
9:38 Sonic and the Black Knight (vs. King Arthur)
10:17 Sonic the Hedgehog 4 (Splash Hill, Official Re-Imagined Remix)
11:00 Sonic Colors (Planet Wisp)
11:42 Sonic Lost World (Windy Hill)
12:21 Sonic Mania (Mirage Saloon Act 2)
13:11 Sonic Forces (Sunset Heights)
13:55 Sonic Frontiers (Cyber Space 1-2: Flowing)
14:40 Outro