Frankly, determining whether Sonic 3 & Knuckles is one game or two separate games is, in this case, a matter of personal opinion and semantics. It just depends how you look at it. Aeolus Aeneas is right in that, yes, they were released as two separate purchases, and as such they are two games. Alan Heer is right that if combined they make one gameplay experience that is the canon game, as it were, and Krisan is right that it's one game from the perspective of the creators, but due to constraints had to be released in two episodes.