Best game since Portal
"Easy to learn, difficult to master" is a good way to describe the gameplay. The first few levels are fun and easy and satisfying as they introduce the mechanics. Later on there's the need for serious strategy and planning.
Also, the UI, art, music, voice acting and story are all incredibly polished for a $20 game.
If you're getting tired of super graphics tech demo FPS games with no soul, and want to actually have some fun playing a game I'd highly recommend this title.
I'm not sure why Gamespot is requiring me to write 800 characters in my review. I've already said everything that was on my mind.
I'm still a few characters short so, uhh, don't take any wooden nickles; and stay in school kids; winners don't use drugs.