Very possibly the best non-multiplayer computer RPG ever and one of the greatest computer games all around besides.
The story is very unique among computer RPGs, and is told masterfully during the course of the game. Oh, the characters! The supporting cast of NPCs found in this game is truly unique and wonderful to behold. From Morte, the talking, flying skull, who is the first "person" you meet to Nordom, the programmable rogue Modron and Vhailor the animated suit of armor there is no shortage of unique characters, and these are just some of the ones that you can have in your party, let alone the ones that you encounter during the game. The main character (the aptly named "Nameless One") is, for a character that you initially know nothing about, remarkably interesting, and you actually have a lot of options as to how you can play him through the game.
If you are familiar with the old Dungeons and Dragons Planescape Campaign Setting then you are already familiar with the backdrop for the game, if you are not, then this is an excellent introduction to a very cool Campaign Setting (I only wish that it was still supported both with new PC games, new books and with new material for the pen and paper game). The setting is probably unlike any other that you have experienced, and is truly a joy to explore.
The game play is a la Baldur's Gate, with a few variations (mostly relating to the Nameless One) which give it it's own nice little touches. You can play the game in a very heavily combat oriented style or in a more puzzle solving/dialogue oriented style, or whatever mix suits you. No matter how much you use your wits though you will fight quite a lot, which is just fine since the combat is smooth, fun and makes sense. You can pause frequently if you want to take a more tactical approach to combat (which somewhat softens the difficulty, particularly when directing multiple characters independently) or you can let it run through in real time for more challenging battles.
I really can't say enough about the game without sounding redundant and like a silly fanboy. You really just have to get it and play it. Even if it means running it on an older system, in a virtual machine or with whatever compatibility tweaks you need to make (the one problem for new players of the game is it does have some problems with running on newer computers) you need to do it. This is simply a must play game for anyone who considers themselves any kind of gamer, whether you like RPGs normally or not.