No offense but read the whole post before typing away.
I said, to quote: ME had plenty of planning and lore built around the first game that heavily informed the next 2 games
In that case, take your own advice and re-read my post: The problem wasn't that ME was a trilogy, the problem was that it was a trilogy with zero planning.
I won't take offense if you don't. 
TBH I think that's what they did try to do whether it worked successfully or not I think it's up to us to decide individually. Personally I had no problems with any of the 3 games. I enjoy each and every one of them and have played them countless times and will play them many more
I think it depends on what they're going for though but maybe we'll get some hints as t whether it'll be a trilogy or a solo story when Andromeda comes out and we get to play it.
Maybe they tried, but I certainly don't think they suceeded very well.
ME1 stands on its own but it's clearly supposed to, given they didn't know it would catch on. Interestingly enough its role in the trilogy is weakened somewhat by the change in tone/style (more military semi-hard sci-fi to more comic book-y space opera) as well as the massive retcons to, and subsequent irrelevance of, some of its biggest plot elements; Sovereign and Vigil.
ME2 might stand on its own but fails as the middle entry of a trilogy- the sweet spot is to be both.
ME3 for all the claims that it's the best place to start is anything but. People trying to play it in a vacuum are probably confused as hell.
Basically before they even started development they should've decided whether it's a trilogy or not, what the overarching plot is and where they want to take it. Then they should focus on making each installment stand on its own while contributing to the overall plan. It may be cliche at this point to cite this as an example but basically take some notes from the Marvel movies. Everything stands on its own but is part of a bigger universe and is building an "overplot" which will be resolved in the Infinity War Duology.