An AWESOME game. Firstly intented to be an enhanced version of Sonic 2, it was later reprogramed as a remake of Sonic 1. This CD-ROM enhanced version featured time travel (you could travel between past and future), and instead of Chaos Emeralds you had "Time Stones".
Also in the European and Japanese version, the music was composed by a famous japanese group, with styles going from Rock to rap, with some hip-hop, classical, pop... (Sonic CD OST was a big hit in Japan).
At last, but not least, the opening and ending movies, using THHU-VIDEO system, were made by Bird Studio (Dragon Ball's studio).