If you want a really great game, go for Deus Ex. It is a lot more than an FPS, your character gets skill points as you move forward in the storyline and complete missions, and you can choose which skill to develop (there are lots). Your level of certain skills decides the accuracy and efficiency of your weapons and tools, so based on what skills you have been developing you will have many different ways of solving a mission. The storyline is pretty much linear (there are three choices at one point toward the very end that change the ending slightly, but nothing significant), but because you choose whether you train your character to be a Rambo or an invisible, superfast spy, the game plays differently for everyone. The graphics are a little outdated (Unreal engine), but the game still looks good.
I loved it. Played through it twice. Planning to do it again sometime. One thing's for sure, you will not finish it in a weekend. Deus Ex will keep you busy for a long while.
Oh, and the story is great!!! None of that "aliens take over your planet, go and kick their butt" stuff, you can tell that a lot of effort went into creating a story that will keep you in front of the screen, wanting to find out what will happen next. You have to do some talking too.
Deus Ex 2 is already in the making too. That is another game to keep your eyes on.
Have fun!