Why the hell would I do that? I want to play System Shock 2, not Fan Shock 2 lol.
Entirely up to you.
The fans have done a great job in up-rezzing the original textures and some of the original models so that they look better on modern high resolution displays. It's the same game, it just looks a little nicer.
Sure, there are also fan mods that change the game ... but I personally avoid those.
If the purity of the original is what floats your boat, then I'm going to assume that you're also going to play it on a CRT monitor with Win98 on a 1GHz Pentium, too.
If so, good for you! That's how I played it back when the game first came out.
These days, on a high resolution monitor and a fast PC, I choose to play the game with some of the upgraded textures and models, and that's how I'd recommend someone new to the game actually play it.
It's not going to offend me at all if you choose to ignore the advice.