Before I read the spoilers, I want to put down my thoughts about the ending of Mass Effect 3. I heard that there was a great deal of consternation and dissatisfaction with the ending of the game. People were saying that it didn't matter what they did at a certain point, they would get to the same ending - which was inevitable.
I disagree that the ending was bad, and I discount the complaint that any sort of behavior in the game made not enough difference.
It was when I finally battled the Ninja dude at the Illusive Man's headquarters that I realized that I had taken the step that pushed me over the edge of the story into the concluding parts. It was just before I did so that I decided to be a complete renegade. I felt that after the fall of the Asari homeworld that there was no reason to be anything but survivalist. After all, the Asari were pretty badass. So from that moment on, I started to get tingly about what might happen next that would sour so many gamers on the conclusion to ME3.
It finally seemed to me that in London there might be one more boss battle against the main Reaper whose defeat would make the rest run away, or that suddenly that defeat rallied Earth troops. But it wasn't that bad ending. Then it seemed to me that the Crucible would destroy Earth as well as all of the machines in the galaxy, something like the dreaded Halo firing. No it didn't go pear shaped that way. Then, as I approached the beam in London, I thought maybe Shepard would die and the story would have no resolution - naah. Couldn't be that, but it came close.
The end that happened was good enough, but also confusing enough not to have been supported by the ledgends and dialog in the playing of the game. In other words, it kept me guessing, and now gives me time after the end to consider whether or not it sits well with me. Let me immediately contrast that with Skyrim.
In Skyrim, all you have is the fate of Skyrim, relatively speaking. There was no do or die situation - and so its main quest could be completed and you could still have things to do. This was not the case for ME3. And in that way there was but a singular destiny for Shepard, the consequences of which changed everything. The Reapers were so overwhelmingly successful that their conquest was part of a cycle, and this cycle had to continue or the galaxy would be transformed. This was the revelation that was flubbed with the Illusive Man and finally given to the Catalyst-Child, and yeah that was kind of awkward if logical. But it all ended up with Shepard shutting down the Reapers via the Crucible because that was the only way Shepard lives to the conclusion - a conclusion which he couldn't live past.
I think it's safe to presume that the Normandy landed on some planet other than Earth. It could have been made a bit more clear that the Crucible forced the Reapers to flee the Earth and then chased them down with a secondary blast of some sort and it was this secondary blast that blew the Normandy out of the sky. But that's a minor dig. The point was that it laneded in the next Eden in a galaxy with no mass effect relays.
Now that I think about it, this is rather like the ending of Fire Upon the Deep, which I finished a couple weeks ago.
Anyway, there's no DLC and the Mass Effect galaxy is dead, which for all the advanced fighting controls, got a little tiresome by the time I got to London. On the whole, the game held up well, and allowed me to get through it without being bogged down by tiresome intrigues and side-missions unrelated to the big picture. I can't tell you how annoying it used to be finding planets and buying probes and looting eezo just so I could fix something on the Normandy or amp up a pistol. I liked the characters better in ME2 and solving their problems was more interesting than listening to Anderson and Hackett jabber on. But that drove the plot that had to be driven.
In conclusion, it did really have to end this way, and because it did and because Shepard had to live to the end, the inevitability of shutting down the galaxy had to happen. Interestingly enough, I think it makes the Geth and the Quarians the new rulers of the Galaxy, as they are more accustomed to living in far flung spaces without contact to the Council.