But DAO explained those things just fine.
In some cases, yes. In other cases, not so much (like Morrigan's god baby). The DLC didn't really help either.
Because ME3 isn't the last ME (just the last Shepard story), leaving some things open ended is fine.
Again, you're assuming that ME4 will resolve anything. For all we know, it could be a prequel to the Shepard series.
Why must everything have perfect closure and a neat tie-up of all storylines?
Because that's what constitutes a good ending to an RPG, especially one that takes place over the course of multiple games and emphasizes long-term consequences.
Writers don't want to write themselves into a corner, but it's clear that you're not concerned about that. Well, life is full of small disappointments, and this is one of them.
Ahem. You
have seen the endings to ME3, right? I'm pretty sure Bioware has already written themselves into a corner, only they managed to not satisfy anyone in the process.
The real issue here isn't that people don't like the ending, and the people that don't mind it (or at least, don't mind it much) aren't telling anyone that they have to like the ending. The issue is that people are blowing it way out of proportion and creating all kinds of crazy plans of action that would be much more productively channeled towards real issues, either in video games or in the real world.
While I agree that threatening to sue Bioware and calling the FTC is a bit ridiculous, nobody here has done either of those things. We're simply explaining the numerous flaws with ME3's ending, while you adamantly defend it for no apparent reason.