Dr. Doctor wrote...
They liked the story but Casey Hudson remarked that looking back introducing a squad where anyone could die in the second game made writing ME3 a lot harder. Pretty much "they could be dead" is the major reason for the ME2 squad getting sidelined, they couldn't figure out a way to make them work so they just didn't put in the effort.
Tbh, I imagine the biggest impact of the Suicide Mission is having to do everything twice, which makes it harder to make big decisions matter.
If you didn't have to have, for example, Grunt's Mission with Grunt *and* Grunt's Mission with Replacement Character, then you could have the mission adjust according to some other variable (like killing or saving the Rachni Queen, or something along those lines).
But with Grunt being killable in ME2, you would then need to have FOUR versions of the mission to involve some other choice or variable. And that quickly becomes impossible. So, I think the feeling that choices don't matter as much as they should is the biggest impact.