Sonic and Knuckles Collection used music from Sonic 1, 2 and 3. Gems Collection had it's museum theme playing, or an incredible noglostic Sonic Heroes remix if you've beaten the game. I know, you're probably thinking, 'How can it be noglostic? Heroes just came out!', but... I don't how how the hell they do it. If you listen to it, you'd understand. It's hard to explain.
Believe it or not, I actually do have an emotional side to me. And as cheesy as it's going to sound, Sonic is somehow linked to that side in a way I, again, can't explain.
So, maybe the ending is why I like Gems so much? I don't know. Possibly. All I know is that I goddamn love it, and I would go to say it's my favorite game of all time. Compilation or not.