Here is the full list of all 12 Pac-Man achievements worth 200 gamerscore. It takes around 1-2 hours to unlock all of the achievements on Xbox 360.
Eat the Cherries that appear after eating a set number of Pac-Dots in Round 1!
Eat the Strawberry that appears after eating a set number of Pac-Dots in Round 2!
Eat the Orange that appears after eating a set number of Pac-Dots in Round 3 or 4!
Eat the Apple that appears after eating a set number of Pac-Dots in Round 5 or 6!
Eat the Melon that appears after eating a set number of Pac-Dots in Round 7 or 8!
Eat the Galboss that appears after eating a set number of Pac-Dots in Round 9 or 10!
Eat the Bell that appears after eating a set number of Pac-Dots in Round 11 or 12!
Eat the Key that appears after eating a set number of Pac-Dots after Round 13!
Eat all ghosts in succession after eating a Power Pellet!
Clear the beginner level by completing the first 5 rounds!
Clear the advanced level by completing the first 21 rounds!
Eat all ghosts four times within a stage!