I've gotta say, it's probably one of my favourite games ever.
To be honest, I wasn't expecting anything special, but even though it's pretty much on rails all the way though and isn't a particularly long game, the story, graphics and gameplay more than made up for it.
I was just so impressed by the variety of missions, particularly the bombing from the plane, sniper mission and the part where you "wake up" after the nuke has gone off, then just crawl around a bit until the darkness consumes you.
There wasn't a dull moment in it. I actually played it through to the end, and have since completed it a few more times - a rare thing for me to see a game out, even rarer for me to go back to it.