I've covered this game once before (it slid in to the #11 slot on my favorite games of all time list) and Scotty made a post a couple of days ago, so I'll keep my entry brief.
The levels are beautifully designed, and truly immerse you into the planet you're on. Whether you're stabbing a Geonosian in the face or fighting alongside a gigantic Wookie, you'll feel like you're right there in person.
If you haven't given this game a shot, you're missing out. What are you waiting for? Do it!
Knights of the Old Republic - (Xbox)
Knights of the Old Republic is not only my favorite star wars game, but one of my favorite games of all time. Yes KOTOR 2 is probably a better game overall, but I personally enjoy the first game the best. I love how they took the Star wars world and turned it into an RPG with an amazing story. From start to finish this game keeps you wanting more.
Bioware is my favorite developer of all time, bringing us Mass Effect, and dragon age, but one of their first was KOTOR, and they hit a home run.
I love traveling across the galaxy and fighting with and Jedi alike. My favorite thing though is the ability to choose light or dark side. I could go on and on about this game, but I recommend you just play it.
Dark Forces (PC)
This was the first FPS game I ever played. I had seen and heard of Doom, but knew my parents would never let me play that. One day, while browsing through the store, I spotted Dark Forces. The pictures on the back of the game resembled what I had seen of Doom. I knew this game was meant for me.
Dark Forces introduced us to the character Scott brought up in an earlier entry, Kyle Katarn. This is Kyle Katarn pre-jedi training. He is rebel special forces secret agent. He is given missions in the background of the Star Wars movies story line. The primary goal is to investigate and stop the development of the Dark Troopers.
Dark Forces has a compelling story line, fun gameplay, creepy Star Wars music and a scary atmosphere. The weapons are fun to use and cycle through. The enemies are challenging, but fair. I can't exagerate the importance Dark Forces had on my gaming life. If you haven't played it, find it and give it a try. I recommend the PC version over the PS1 port.