On a serious note: I think the Earth-scenes are just some illustration of an ongoing invasion in all of "Light-space" In future trailers we wil probably see the impact on other planets.
I'll go out on a limb here, and speculate like mad:
Imagine, the soldier You're seeing is recruitable, and that the ME3 shepard or some offspring, will be travelling to many besieged planets to get the best team-mates. I can even envision that the (now transformed by Legion's virus ,might the player have chosen that) Geth-homeworld is the only one holding off the Reapers, {--- because the Reapers, themselves being non-organics/machines gone bonkers, fear a world-wide artificial machine-brain, given that world-brain could be their equal and spam them to death or something..

---} and are harbouring the Quarians that survived the initial attack on the migrant-fleet by the reapers..oops..did I say that out loud:pinched:?? It seems logical ,because I read somewhere that Bioware wanted to resolve the "Quarian-thing" in ME3 as part of the story.. Shepard WILL need Quarians if he wants to succesfully build the super-relay to get to the Prothean home-world.
Part of the end-battle will be fought in the Local Cluster, but Bioware cannot go too fantastical with our well-known neighbouring planets..soooo..I truly think the final giant battle will be after the team has gathered masses of clues all over the galaxy and finds the home cluster/world of the Protheans(say, via a new Omega 7 -for luck- relay, constructed out of parts hidden all over the galaxy by the Protheans..parts&clue-gathering is standard lore in RPG's, so, why deviate?), and consequently get the ultimate weapon, which in turn ,combines with human and turian, quarian, whatever ingenuity to wipe out the Reapers for good.
Seems the most logical chain of events..
just my 0.02 credits..
[edited for clarity]
Modifié par diakrite, 15 décembre 2010 - 01:33 .