Single Status Update
It depends. I see "poorly written" as code for "there were parts I didn't understand" (which incidentally, could be a valid argument), as well as, "I don't like the way it was written". "Poorly written" to me means that it either failed to accurately/adequately use writing convention (i.e. a story that tries to be good, but fails) or that it relied too much on archetypes and/or over-used themes (a story that paints by the numbers).
Good writing on the other hand successfully breaks from convention or turns convention on it's head. TSL did a lot of the latter. The first game gave us lots of clear black and white and the second spent a lot of time telling you that white was black or vice versa. ME3 did the former. The end of a game is supposed to have a boss fight where the hero wins and everyone lives happily ever after. We didn't get that. We didn't get the conventional ending so people equate that with bad writing. 20 bazillion Twilight/Reality TV/Michael Bay fans can't be wrong.