Honestly only room for improvement here. The OG writer for ME wrote ME1 & 2 with ME3 being a guy who supposedly squabbled with him over details and abruptly changed course and retcons, and some even trying to put some of the worst ideas of Andromeda as stuff he passed on for them to use (note: this last one is mostly speculation without real proof to best of my knowledge)
Recent, last 10 years or so, Bioware games have not had the quality of writing they were known for in the 90s and 00s, with some charitable takes on TORs overall writing as being very shotgun approach and seeing what sticks and the fans react well to rather than a very clear end point in mind from the start.
The ending to 3 was a bit of a cop out and generally out of line with the narrative of the game up to that point. Everything proceeding that was fantastic though. Still an 8/10 in my book
Lead writer left after 2 and his replacement was kind of known for not getting along well with his predecessor. So its still not clear if he intentionally made changes to the plan that had been put in place or if he just never actually read the design doc that had been left for consistency.
They canned the writers from 1 and 2 and promoted this goober who said that "Twilight was good writing" to finish the 3rd game.
Which is why we go from having Shepard being such a badass the Reapers tried to make a reaper version of humans, to all of a sudden being all PTSD about shit.