At any point in the game, if you leave Sonic standing perfectly still (without pausing the game), after three minutes he'll say: "I'm outta here!" and race off the screen. This ends your game.
This game features the first appearances of both Amy Rose and Metal Sonic, who is by far the most popular and well-known of all the Sonic robots.
The US release of the game was held up a few months while a whole new soundtrack was being produced by Spencer Nilsen, who was behind many other major Sega CD soundtracks, as well as a few early Saturn scores. But alas, the new tunes received much flak from purists who wanted the original Naofumi Hataya and Masafumi Ogata score left intact. The battle wages on even today.
In the instruction manual for the US version, Amy Rose is referred to as "Princess Sally". This was probably intended to tie in with the newly released cartoon "Sonic the Hedgehog" (1993) and the comics, although being that the character of Sally was already established, the only thing it achieved was to shove Amy out of the potential cast completely. However, she did become part of the supporting cast in the comics years later.
While most of Sonic Team relocated to The Sega Technical Institute in San Francisco to develop Sonic the Hedgehog 2 (1992), Naoto Ohshima stayed behind in Japan to develop Sonic CD.