How big of a factor is lag in shooters, really?

I ask, because I'm at 300 kb/s download and 150 kb/s upload, and I can't seem to score better than a 1:1 K/D in most online shooters. This always seemed odd to me. When I'm playing, someone will come around a corner and I'll be dead in less than a second, before I even see or hear bullets. When I watch the killcam, it'll show they stood there and fired at me for at least 3-4 seconds uncontested.

Is that a common experience, or is it due to my ridiculously slow internet connection?
 


My ping ranges from 90-100 at the low end (ie, The Killing Floor), and around 300-500 at the high end. It usually seems to average around 150-200 in most online games like BF4 or Black Ops 2.

No, I can't really test at a friend's place. I have no friends. :3
 


Yep. The problem's not with tech on my end, it's with the ISP and my location. There's not really any better internet offered way out here. o_o
 


Ouch. You're better off camping / sniping than trying to meet people head on :(
 


I mostly just stick to cooperative games when I play online.