A game that if it were fantasy would be No.1 above Morrowind and Daggerfall!
It uses voxels so doesn't use your graphics card, this means it needs a powerful CPU (1ghz+) and lots of RAM (512mb+). Something that we have today but didn't 6 years ago when this game came out. This means if you find it today and buy it you will be playing it the way it should have been played back then! And lucky you!
After a great 20 minute (it seems!) intro you find out an experiment has gone wrong and a vortex has opened up between Earth and a world called Aldepha. You have to travel to Adelpha with two scientists and an exobiologist (who you have a history with!). On arriving your comrades have disappeared and the locals think you are a god come to save them from an evil dictator. It is a little information heavy at the start, but preserve a little and come back to the initial location a couple times to get the info again when it will gel better and you will be off on the greatest PC adventure you have ever played! It will suck you in and before very long at all you will want to save these local inhabitants!
It is 80% adventure, 10% RPG and 10% shooter. In fact a lot of the time you can avoid the shooting by being a little stealthy. The fighting is strategic as the enemy AI is very sharp, with groups splitting with one calling for help on a trumpet like alarm (and trust me, if another patrol hears it they will come to help!) one coming straight at you and two trying to get around you with flanking moves. They are quite happy to change weapons in mid stream to get you better! For a game six years old. The AI in this beats many modern day FPS's!
I won;t tell you more of the story as it is so engrossing and engaging you need to go into it as open minded as you can!
I envy you playing this game for the first time.It is such an eye opener and so joyful to play it will be at the top of you gaming list in no time at all!