If You complete the indicated task You'll get the allotted gamerscore.
Complete Chaos (25) - Collect all seven Chaos Emeralds.
Complete the Game (25) - Finish the game.
Fast Freeze (25) - Complete the Icecap Zone.
Points III (25) - Score 80,000 points.
Points II (15) - Score 40,000 points.
Marble Finishes (15) - Finish the Marble Garden Zone.
Wet Feet (15) - Run across water.
Wet and Wild (15) - Finish the Hydrocity Zone.
Goodie Gumballs (10) - Get a blue gumball.
Chaotic (10) - Collect a Chaos Emerald.
Points I (10) - Score 20,000 points.
Halfway there... (10) - Collect 50 rings.