After a long day of work or a stressful day in the lab (I'm working on a Master's degree in Genetics) nothing helps you unwind like shooting a few terrorists. I've found this game to be a lot of fun. My brother-in-law played in on the xbox 360 and said it was pretty fun. Since I don't have an xbox I figured I'd take a look at the PC version. The demo is great and I'd highly recommend taking a look at it. It had some sweet modern warfare weapons that make the game pretty intense. If you find that you really like the game you can pick up a copy on ebay for around $20 (much cheaper than the $50 Best Buy is asking). Here is the link to download the demo. It's a big file, but it's worth the wait.
Also, here is a screenshot if you're wondering what the game looks like.