Hard. I died a few times, but they were all my fault. This game is really about getting in the best positions so that you don't get surrounded by the enemies.
The only times I died where it was not my fault were when you get low health and pull out a flare. The camera, for some reason, spins around in dramatic fashion when you have low health and whip out a flare. It looks really cool, but makes escape nearly impossible.
Ammo was either really sparse or really abundant. A hint: use all your specialty weapons whenever you need them. I am a hoarder, but after every chapter you lose your weapons/items/etc, so I was wasting the best weapons.