Multiple ways to score on a level?
Not to side with Sonic Team, but they have that. It's called time, enemies, and ring collection. (Admittedly, enemies killed doesn't exactly put a huge effect on the score like it used to. To be honest, I'm not even sure if kills still add to your score. Either way, there's still multiple ways to score >.>)
You want a score with replayability? That's easy to do. It's called online leaderboards. Thanks to IP, we can have multiples... like
1. World
2. Continent
3. Country
4. Region
5. City
Better yet, there also needs to be a reward for staying on top. Say for example, special items or ring bonuses for the obligatory Chao Gardens thing. Nothing says you're the best in the world quite like a Chao with a Chuck Norris mask.