i am pretty surprised you are saying it isn't very significant when it's more in-depth than most pure shooters.
iirc i said the exact opposite of this! i'm MODERATELY IMPRESSED with what you can do as far as limb-specific shots. in any case while i do like the impact of being able to target specific limbs, i don't think a lot of the other stuff you mentioned has any real impact on the quality of the battle system. like, i honestly couldn't care less if they flinch when i shoot their leg, and i think little additions like this are the last thing you should just a battle system on.
anyway now that you are saying you do not use vats, i really do not know how you play this game. idk if you're playing in on the 360 or the pc, but on the pc the controls are a bit jerky and enemies move around pretty swiftly. combine this with the fact that i am not good at fps aaaaaand the part where many of the battles take place UP CLOSE where you have to pivot pretty proactively to keep them in your line of sight and i'm really surprised you are actually playing SANS VATS. on another note i think many of the guns feel very similar, and i rarely find myself giving a damn about what i'm using, beyond short-range/long-range weapon.
but to answer your question, i didn't have many serious problems with mass effect's combat. i thought it made p good use of cover, i thought the weapons DID feel decently different and each served a pretty specific purpose, i thought it was intuitive, i thought the pacing of the combat generally flowed really well, and i thought for a game made by people who typically make rpgs, it came off as a competent shooter, because it did not feel like a patchwork shooter, just a regular third-person one. the aiming probably had something to do with this, and i liked that too. conversely, i feel bethesda didn't even try with fallout's battle system. they took the one out of oblivion, which was designed almost entirely around melee, added some guns, and threw the vats system on top. it was really unambitious, unimaginative, and it doesn't FEEL like a shooter at all; it feels like i'm playing oblivion and have to use ranged weapons. aside from the ability to take out particular limbs, i do not really find anything about this battle system to be exceptional in the slightest, or superior to mass effect's at all. i really don't think it plays nearly as well. clearly we just disagree here!
wasn't there some weird slow-down thing in mass effect, too, by the way? i feel like there was, but i can't quite remember.