The score for the story levels is measured in one, two, or three stars, depending on the amount of points you earn. You will win the level as long as you earn one star. The challenge levels have a set amount that must be met, without the option of earning more than one star.
Tip: If you can't reach three stars on a level, you can change the difficulty to a lower setting in the settings menu under the main menu, and retry the level.
Bonuses are earned for chains and combos, and for having a clean location at the end of the level.
Side Objectives:
The levels have a challenge to be completed. Challenges don't have to be completed but add points if you do complete it. Each challenge completed earns a diamond.
Tip: Sometimes you can't both complete a challenge and get three stars in a story level. If this happens, you can play the level twice: once to complete the challenge and once to reach three stars.