You can see that the in game shots are much more similar and I put up with the differences. Eventually, I came to just ignore the niggles. I played my Shep how she would be and it worked well. I will now provide my reaction, minus specific spoilers, to the endings. If you wish to stop reading, I fully respect that. Highlight the text to see it.
Now that I've done it I can see why so many people are upset about it. There was a heroism in ME2 as an ending, with moments of loss and regret, depending on your choices. ME1 took it's ending to a point where the magic of the universe endured, as it's successor.
ME3? Bioware talks about closure but I think they're missing something. The endings felt like everything that had been done was moot; you could have sat on your ass as a Spectre and still gotten one of the endings, which were hardly different from the others. Saving the base, your companions loyalty, uniting or destroying races and everything from "Well, what about Shepard?" to the final mission gate in ME3 amounted to nothing more than war assets.
The game itself is filled with heart rending moments and times where you do everything you know you needed to in the previous two games. The endings are very beautiful, especially the "best" ending, perfectly choreographed and executed, given the scenario that appears in the last 15 minutes. But that scenario, in my opinion, defeats the Reapers sure, but also everything that was unknown and untouched about the Mass Effect universe. You'll see what I mean and it is only my opinion but I now agree, it isn't the way it should have gone and I hope Bioware comes up with something more deserving of fans' continued devotion. Until then, I won't be playing again.