So, after playing this for some time, my thoughts on the 'crucial' decisions you make through ME1/2 and their reflections in ME3. Spoilers, obviously.
Well, remember how you saved the council in ME1? And the Rachni? And destroyed the Collectors base in ME2 to not let Reaper tech get into the wrong hands? Well, let me tell you, no matter what you'd do, the outcome would be the same. I'm 100% sure of that. The council or earth council would be as useful as it was always, "Ah yes, Reapers" useful. The rachni would be probably 'found out', despite being destroyed and Cerberus would still be your enemy in ME3, no matter if you'd be a willing pawn or not in ME2. Because as ME3 showed me, the council is useless, the rachni suddenly 'showed up' in one of Wrex's missions, so it's a 'generic' plot mission, not a 'recruit your ally one' so it's just a way to incorporate both decisions into the story without changing it much. And Cerberus would still be axe crazy no matter if you saved the base or not, because they got their own reaper tech anyways!
While this is incredibly lame, I do have to feel some respect for the writers giving so much ambiguity to the outcomes that no matter what you do, it can be used both ways satisfying the players on their first playthrough. Well, that's what I think.