Last time we left Gordon Freeman, the unlikely scientist-hero from the first Half-Life, he was traveling. Yes, just traveling. The mystery was where he was traveling to and why all of the incidents at Black Mesa had happened.
Half-Life 2 begins with Gordon arriving via train with the G-Man teasing his mind with sickly whispers of warning. The last stop of the arriving train is City 17, a bastion of the alien Combine forces, yet another mystery themselves.
For the rest of the story, you'll have to play the game yourself. I'm absolutely certain that getting through this game will be a really good experience. That means that i wont give you any spoilers and just leave you with the mistery. Suffice to say, there are lots of twists to curl your brain along the way, some a bit more predictable than others, but all welcome and interesting.
The system that I played the game on had these specs:
ASUS P4C800-E dlx motherboard
Intel P4 3.2GHz CPU
2.0GB DDR400 dual-channel RAM
Radeon 9800PRO 128MB video
Creative Audigy 2 ZS sound
Western Digital 160GB SATA HD