I've always been somewhat annoyed at Mass Effect not being able to decide whether or not mass relays are absolutely necessary to get around, or not. I mean, starships can get to FTL on their own; you zip around star systems light years away from each other without using mass relays, which are more used as galactic highways between different areas of the galaxy. So considering how you get around on the galaxy map in all 3 games, one could deduce that nobody got stranded anywhere - the fleets merely lost a quick way to get to distant parts of the galaxy.
But then there's Vigil's description of how the Protheans got their clocks cleaned in ME1 - first the Reapers locked away the relays, everyone got stranded where they were, so there was no organized resistance; the rest was just centuries of Reapers cleaning house. Sure, being unable to use mass relays would have made it difficult to organize any sort of massive counter attack, but it doesn't seem to me that all the fleets in Earth orbit would have been downright stranded.
I can understand the "let's leave something to the player's imagination" ending to some extent, but leaving us with literally nothing is plain retarded. Someone thought he was being deep, and that someone was incredibly wrong, and just demonstrated he didn't understand what his own product was all about. You don't get the player to spend years making decisions of galactic importance, getting attached to characters, to throw it out the window at the last 10 minutes because it's time to get deep, dark and serious. In my opinion, they got vague at the wrong part. They explained the purpose of the Reapers, which was incredibly simple and disappointing. Someone decided that organics will always make synthetics which will in turn always wipe out all organics (apparently Geth and Edi fighting alongside organics in my cycle didn't make the kid avatar reconsider that theory).
So the solution is to use organics to melt them into goo which is used to make synthetics that wipe out all organics. Seriously? This was the Reaper's purpose that we spent 5 years listening about it being incomprehensible to our feeble little minds? It's not that incomprehensible, it's quite simple, and to be honest more than a little dumb. What they should have done instead is leave us in the dark about the purpose of the Reapers, maybe leaving a few hints here and there but making their motives dark, mysterious and incomprehensible. Where they should have been clear is the ramifications of the last 10 minutes of the game for 1) Shepard and his squadmates, 2) Earth and the Galaxy. I'd have been happy with that. And the effective war assets number should have impacted the game so endings include:
- very low EMS: worst ending. Earth destroyed due to Alliance being pretty much on it's own in the battle. Other races are to follow, Shep is dead, Reapers won, cycle repeats after advanced civs are gone.
- low EMS: bad ending. Reapers destroy Earth, Shep dies, but the other races got enough time to consolidate a counter attack which eventually drives the Reapers out. It's unknown when they'll return.
- medium EMS: Cycle broken, Reapers destroyed, but at the cost of Shepard, Earth and humanity.
- high EMS: Reapers destroyed, Earth survives, but Shep and his squadmates make the ultimate sacrifice to make it happen.
- very high EMS: All lived happily ever after. Reapers get destroyed, Alliance builds a new citadel in Earth orbit, Shep makes loads of blue children, Garrus moves to Omega to have a regular testing ground for gun calibration, Conrad Verner becomes Alliance councilor (touch of social realism here - always have the most inept grab the high political positions

).