Cheevers looking for a quick 200 Gamerscore should steer clear of Mega Man 10, because the achievements it offers will be, per the usual, hard won. Of 12, all but three or four seem impossible to me.
And the top payoff, "Mr. Perfect" - beat the whole game without taking any damage - delivers a paltry-by-comparison 30 Gamerscore. But at least it's six times the payout for what you get clearing the game once, by any means.
Here's the full list:
Whomp Wily! (5)
Clear the game once.
Blue Bomber (10)
Clear the game in under an hour.
Clear the game on hard.
Hard Rock (20)
Make it to a boss room without getting damaged.
Defeat the 8 bosses without your helmet on.
Defeat 1000 enemies.
World Warrior (5)
Defeat one of every type of enemy.
Trusty Sidearm (20)
Defeat the 8 bosses with just your default weapon.
No Coffee Break (10)
Clear the game without using any energy, mystery, or weapon tanks.
Clear the game without continuing.
Clear the game without dying.
Mr. Perfect (30)
Clear the game without getting damaged.
Mega Man 10 Achievement List [Xbox 360 Achievements.org]