Different Ending Poses
Normally after beating the game, Sonic will strike a jumping pose similar to the one he does at the end of Sonic 1 but if you collect all the rings during the ending sequence, he will either do his fist pump pose from Sonic 2 and 3 ending or turn into Super Sonic if you also have all emeralds.
Sneak-Peak for Episode 2
Beat the game with all 7 Chaos Emeralds. You'll get a sneak peak at something that will be in Episode 2.