That's an awful defense for the game. Incidentally, the way in which Mass Effect 1 differs from other shooters is that its mechanics are just bad. The controls aren't tight, the levels barely deserve to be called designed, the weapons felt very homogenous and shared the same flimsy feel, and enemies lacked tactical variety.
No it's not. Saying "the controls aren't tight" or "weapons are flimsy" (whatever that means) is just a bad descriptive term. Sounds more like you are talking about presentation or flourishes. The mechanics are fine, but the shooting is not just "leave your finger in the trigger while running" kind of shooting, like said, it's volley based and power management is way more important. The weapons were not homogeneous unless you didn't bother customizing them with different mods and ammo types. When people talk about RPG elements lost is about those statistical and functional variances given by those items. Making a mini-nuke heavy weapon vs a grenade launcher with no modifications possible instead is the RPG vs Shooter design people usually complain about. You prefer one, that's fine, that doesn't make the other one "wrong".
Not really. I found that the most optimal strategy every single battle was to just spam every power you had steam roll over your enemies. Team composition was irrelevant, and leveling required little thought. I'll grant you that levels weren't corridors, because they were worse: simply rooms connected by short hallways with rectangular bits strewn lazily about them. ME 2-3 benefitted from more linear design because then the levels actually had a good sense of pacing to them.
I'm sure you played like that, but it isn't the most "optimal strategy" just because you did. Most of the times they were more open areas, so your "connected rooms" complaint sounds false anyway. Go play it again.
The game had atmosphere and plot, but it's mediocre in nearly every mechanical category.
Call it what you like, it was fine and any ME (including 2 and 3) was a better game for its atmosphere and plot than for whatever mechanical improvements they tried to do like scanning planets or buying fuel and running from tiny reapers in the galaxy map to make up for the lack of exploration.
Tali and Garrus were far more interesting in the second game. ME1 Tali was practically a glorified codex entry. But yeah, name the worst character in ME2 to make your point, I'll be over here with Legion, Mordin, and Jack.
Like I said, Mass Effect 2 focused on character development almost exclusively, and had for more characters, many who benefited from already being introduced. I liked Legion and Thane and Mordin, etc. Saying Garrus wasn't Garrus until 2 is just ridiculous, tho. His whole personality, dislike for authority and loyalty was there from the very start. His mission wasn't as elaborate as the ones in 2, but you got to know him through it all the same. Wrex and Ash and Liara and Garrus were all themselves since 1. Of course they are going to grow with more development in subsequent games, that's just common sense. It doesn't make the particular character writing unoriginal in any cases, i.e. daddy issues for everyone.