Lost Patrol
Lost Patrol was a 2-player board game designed by Jake Thornton and produced by Games Workshop way back in the day when they still did other things than cranking out new editions and codices for Warhammer 40,000.
Gameplay
One player takes control of a group of Space Marine Scouts (the eponymous lost patrol) trapped on a jungle Death World. His goal is to find the Marines' dropship and get the fuck off that hellhole. The second player controls the local fauna. His goal is to cackle maniacally while the Scouts drop like flies.
The game is played on a modular map consisting of hex tiles that is continually expanded as the Scouts move along. It is so ridiculously unbalanced that even finding the dropship is considered a major victory for the Marines. According to Thornton himself, this is intentional and part of the fun. The only way make Lost Patrol "fair" is to take turns at playing the marines and see who gets eaten faster.
Availability
Original copies of Lost Patrol are reasonably easy to find, but if for some reason you can't be bothered with tracking one down, you can easily simulate the experience of playing the Scout side by pulling a burlap sack over your head and having a buddy lock you into a small room filled with feral cats.
Lost Patrol Today
While the game is no longer produced or maintained by GW, Jake Thornton has recently published a FAQ as well as a couple of new rules on his blog.