The games are based on the engine from the game "Nocturne," and, in fact, some characters from that game make appearances in the first Blair Witch game. The game is basically pre-rendered backgrounds with polygonal characters. It's not a horribly taxing game so as long as you have a decent rig it should be fine.
I only played the first one (as the reviews made it seem like the other ones were more action oriented and I'm not good at the action aspects of the "Nocturne" engine and gamepla), but I really liked it. Cool story and scary as hell in some places, play in the dark, with headphones!
There are demos of at least the first two games available as well. I don't remember the company website, but perhaps check download.com to see if it's available there if you want to try that first.
