This is one of those games that got me to keep coming back because it captured the essence of player stress & player fun perfectly. The game ramps up nice, movement feels great, and each weapon feels unique in its own right.
I still haven't finished it but I have been getting progressively better as I'm learning the weapons you put in to the game. I really liked the subtle UI touches with the splash of color for ammo also being the shadow of the weapons they correspond to, as well as the audio changing from upbeat to ominous as darkness sets in. It actually took me a second playthrough to realize the audio thing because I was so focused haha.
A great example that you don't need hi-res graphics to make a great enjoyable game.