Story. Even a good action game needs to have a greta story. You can have bad graphics and a crap engine, but if the story is really good, people will overlook your flaws.

humor, but not over kill.
At least one big bad kick ass weapon.
A really good evil guy.
Good interaction.
Able to move anywhere.

sexy girls!

But you can't just throw them in there like in a car magazine, they have to be well-integrated.

A donkey to carry loot