Remember when Sonic Adventure DX threw in all the Game Gear games, including one that was Japan only, simply because “why the hell not”? I miss when compilation releases just got bigger and bigger, with the 360/PS3 era dumping as many games as they could into their collections before they caught onto what the Virtual Console and XBLA were doing and decided making smaller collections/standalone releases would make them more money.
Sega Genesis Collection on PS2 and PSP had over 30 games including a few arcade releases, interviews, videos, artwork/manual scans, and even a small hints/cheats section for each game. Then Sonic’s Ultimate Genesis Collection on 360/PS3 improved on that even further with about 50 games (interestingly, it had Sonic 3 and Sonic & Knuckles, but not Sonic 3 & Knuckles, supposedly due to technical issues).
Honorable non-Sega mention goes to Namco Museum Virtual Arcade on 360. It had about 35 games including a few of the relatively new PSP Arrangement games and XBLA versions of all the games that had them, along with Pac-Man Championship Edition, Galaga Legions, and Mr. Driller Online (these three were practically brand new at the time, and Mr. Driller has since been delisted, making this collection the only legal way to get it now)… and abysmal sales numbers. No Namco Museum since has come close to having that many games.