It's definitely single-player campaign on a Medium/Normal difficulty first.
If it has multiplayer, I might dabble in it for a bit, but I'm not big on competitive multiplayer games (unless playing with a friend, and not against them).
Then I might play it on a harder difficulty if I can be interested enough to do so.
Then it's sporadic play of it overtime. Perhaps try to get achievments, or replay the story, or just do my favourite parts, or just mess around if it's that sort of game.
And if it has cheats, then I'll use those to mess around with at the end.