Uhh.. Jonah wrote...
My guess of how ME3 will go:
Shepard: Oh no! Earth is under attack! I'll need allies! We will need Asari!
The Asari: Sorry, we have our own problems that you will have to help us with before we help you.
Shepard: *Shepard helps the Asari* Now I need help from the Turians!
Turians: Yea sorry, you're gonna have to help us too.
And it will go on.. and on.. until the final mission which will take place on Earth.
I thought about that... but I honestly don't think so. I can't see that being the focus of the game. Sure, you could be right, but I don't agree. I think Shepard has already done what he needs to do to get the help he needs. I think the DLC will lead us up to ME3 and set the stage for ground zero (think God of War III). It's ok to start minute 1 of a game with huge plot elements.
I'm hoping that the vast majority of the game will take place actually fighting the Reapers, and the decisions made in 1 and 2 will affect how the gameplay works (fighting with Rachni, Krogan, Quarians, etc).
Or... it could be that you spend the whole game acquiring resources and allies and you have a big counter on your loading screen that says 6.5 billion expected casualities which goes down the more side missions you do (kidding).