Street Fighter 2

The answer has to be Street Fighter II. Improving on a little-known original game to essentially redefine video games for the next 8-10 years. – ultramattman17
[Street Fighter 2] might be the closest thing to a “right answer.” – Adam J
Lots of good calls in this comment section, but the best sequel is Street Fighter 2. Everything else is just hunting for 2nd place. – DrugBust
It’s hard not to default to Street Fighter II whenever I hear this question. It’s really difficult to top it in terms of how much it improved upon the original. It’s basically the quintessential video game sequel. – StealthMantis