Before all that, unless you're importing an existing Shepard, you'll have to make a brand new one, fiddling around with your eyes and nose until they look really strange, picking your class and backstory, and telling the game a little bit about some of your actions in the previous adventures - who lived, and who died, for example. Then you have to decide which of three different versions of ME3 you'd actually like to play.
Your choices are pretty simple, thankfully. Story mode dials down the combat but allows you to make all the big decisions throughout the game, choosing what happens at crucial - and not so crucial - moments, and who you end up making sweet, slightly creepy, dead-eyed zero-gravity love to.
Action mode offers you exactly the opposite experience, turning conversations into standard non-interactive cut-scenes, while providing you with a straight-up cover-based shooter, with no morality nonsense to get in the way of the headshots.
Role-playing mode, finally, is the traditional Mass Effect mode. If you're reading this, it's the mode you'll almost certainly end up playing. (If you're not reading this, what's on telly at the moment? Is it time for Diagnosis Murder yet?)
edit: ah, it wasnt even a video, then i have absolutely no interest.