Salsa_Shark: I can see by your avatar that you are a very big SS fan Fenixp. Which do you prefer 1 or 2.
First one, actually. I have played the second before playing the first (and that was the mistake, I believe I would enjoy second a bit more if it was the other way around), so it's not the typical 'you like what you've played first' kind of thing.
There's much better sense of freedom in first than in second, and even at fifth playtrough, I was still finding new things I have never even noticed before. Also, in first System Shock, you actually FEEL like you're walking on a space station, it doesn't feel like a game nearly as SS2 did. Also there are certain game mechanics that I just find way more immersive. Oh and, of course, there's SHODAN at her best.
SS2, on the other hand, had better story and in some places it's even more atmospheric, which is probly caused by weapon jamming when you're not taking care of them etc. And there are way better RPG elements in here, pretty much fully customizable character. Still, I have finished SS2 2 times and SS1 5 times.