The writing in ME3 doesn't seem bad at all to me.
What it is is it reeks of "lack of dev time" to me. They would rather spend some minutes doing separate VAs to acknowledge past choices rather than actually having past choices changing the world in a concrete manner. I'm still on Tuchanka and I have yet to make the major mission, but the Rachni Queen bit kinda pissed me off. I'm doing a renegade run and my Shep was all like "WTF why are Rachni alive I killed them all" and I could smell development hell from miles away.
And that's just wrong. And you know what? The solution would have been so simple that it pains me. Just scrap the mission altogether, that's all. Less content BUT acknowledgement that your previous choices actually matter, and make standard run (without import) as if Shep spared the Rachni Queen, so newcomers do not "lose content".
The biggest problem in ME3 boils down to the fear by the dev teams of making sure everyone gets every single bit of content, instead of making sure previous choices mattered and changed the world more than a few lines.