One of the best RPGs ever made.
This game can be unforgiving at times (infuriatingly so, even), but there is nothing quite like it; no other game allows you to express yourself nearly as well as System Shock 2 - and imagine me saying that about a game entirely without dialogue choices.
Choose your weapon skills, your equipment, your implants, your character stats, your tech stats, your upgrades, your item usage, etc. and etc. You only get the one go around - play it safe or play it risky - but make it through to the end.
The story, the dialogue, and most importantly, the atmosphere are just a hell of a great bonus.
So cozy up to the fire, enjoy the soothing sounds of a nice audio log, and rearrange your inventory for the holidays while a security droid brings you a cup of hot cocoa.
Get immersed!