Surely not - it is amazing how achievement keep me out of the community games section.

Typically normal - most of the single player acheivements are tied to either beating the level. Some have an additional achievement for beating it on normal so I start there. Then if the game is good, I will run through the most difficult level which is usually unlocked by beating the game and will almost always have its own achievement as well.

I am quite busy outside gaming so there are many games I will just play on easy for the storyline. Depends on the time, quality of the game and length of the single player mode.