Some quick thoughts after revisiting the trilogy. I usually end up choosing male default face earthborn ruthless renegade soldier in ME1, and infiltrator in 2 and 3. I went with the same during this revisit.
TL, DR: ME1 >>> ME3 > ME2
ME1 is arguably the closest thing to a "conventional RPG" in the series, and of course the best game. No contest. The sense of facing the unknown before all the reveals and twists as the young champion of a young race, no less, is tremendous. The talk with Sovereign may be the trilogy's top moment. As far as the systems go, shooting is passable, the overheating system is okay in theory but can get annoying, auto sticking to cover is a tad tricky, and Mako hate is way exaggerated.
ME2 is always praised as the best of the trilogy by journos and normies. Back at its release I played it a ton. In their attempt to get rid of clutter and redundancy, they oversimplified everything. The upgrade system is a joke. Rubbing a firm, round planet for resources and the occasional quick mission gets old really fast. Getting to cover pretty much grants immunity as long as you aren't sticking to the wrong waist-high invulnerable object.
ME3 improved on ME2's oversimplified builds and itemization, however it's so transparent that it was done for the multiplayer mode which of course has those fucking loot crates, where the good rare weapon is just one crate away, and not in the name of are pee gee. Enemy AI is fine for this kind of game, with the implementation of smart flanking and grenade tossing, so getting to cover is not an automatic immunity to everything. Story-wise, there's disconnect between some side missions and the sense of urgency of the main story, which is the case in many games whose main story urge you to DO SOMETHING NOW while offering plenty of side content. On the bright side, everything ends up contributing to the big peepee points here.