First of all, this game can be hard to get in to. Mainly because it's hard. There are some things that you will only learn not to do once you have died repeatedly by doing them. And that can hurt, especially when you are a couple of hours into a run. Permadeath hits hard when the game lasts so long.
But that really steps the tension in this game up a level. The game does a very good job of making you scared, in a few ways. There's a clever viewpoint system that makes tight corridors feel claustrophobic and open areas make you terified of a redguard standing on the other side. I'm impressed by the sounds. At first I was dissapointed that there was no music, but I have learned that it really matters that you are listening out for footsteps, to tell whether there is a giant zombie on the other side of that door or a group of gunmen approaching. I feel that the ambiant sounds of the facility could be more detailed, however.
When you are attacked and are not ready, it's a panic, which is the last thing you want to do. Switching through weapons, trying to remember which one still has ammo left over, trying to work out where to run that you aren't going to be swarmed, and firing off rounds and MISSING! Missing really hurts in this game. Ammo is scarce.
Overal. If you don't want a tense, hard, painful, roguelike that punishes you for every mistake, this isn't for you. If you are willing to deal with that for the immensely satisfying experiance of finally beating those robots of doom, with 2 health left, healing up again and finding enough ammo to last you for ever, you'll like this. I really do. Favourite rogue-like. I think it really starts to shine when you actually get good at it.
Oh I'll give some advice too, for best enjoyment. I'd play the arena mode a fair bit first, so that you don't get disapointed that you died because you aren't used to the controls yet in your first few runs. Then i'd go into the 'story' and have some fun.