The controls has been modernized, it feels like a game that launched this year, but everything else is completely faithful to the original. I've only tried the original briefly, but I've red from people who played both that you could basically follow a guide from 1994 and still be able to get through the remake.

Aside from that, they added a scrap system which you can collect junk, destroy it, and recycle it for coins which can be spent on weapon upgrades. I think that's the only major addition in the gameplay itself, and it's something that was already in a similar way for System Shock 2 with the nanites.