Some folks have mentioned that S2 has a major issue with getting randomly, almost instantly killed, and I've noticed that the main time where this feels really bad is when you're at full shield.
Having an enemy take you from full shield and a chunk of HP to 0 in an instant just always feels bad, and a lot of the time it's very clearly from something that you almost couldn't react to. What prompted me to make this post was popping my head around a corner and having an LMG turret do 2500 damage to me in the space of less than a second because it decided to buzz me down with perfect accuracy at random. I was not sprinting around willy nilly outside of cover--I straight up poked my head out to fire a single shot and got turned to dust before I could blink.
Another really frustrating situation is when multiple enemies all suddenly converge fire on you at once. For instance, you're dodging bullets outside of cover just fine, and the enemies are missing you with stormtrooper accuracy--until they all line up a shot at the exact same time and chunk your entire healthbar out of nowhere!
I think that the best way to deal with these huge damage spikes in a timely, simple manner would be to implement a shield gate for massive damage. If your shield is at full and you take your entire shield in less than 1.5 seconds, you should be provided a brief window of ~0.75s invulnerability that will only recover again when combat ends and your shield is fully recovered.