One of the announced games to be featured alongside the upcoming PC and console versions of Half-Life 2: Episode Two is one that promises to obliterate your concepts of traditional level design and generally assault your brain with a large rolling pin. It's called Portal and, should the name not be explanatory enough, it deals primarily with gaping holes in time and space which magically transport you to different locations. Where Human Head's Prey took you for a wacky ride through these portals, Valve's title equips you with a sterile looking gun and urges you to make your own entry and exit points with wild abandon.
The trailer (embedded in the second part of the post) aptly demonstrates the powers of the portal gun, the dangers of getting caught in an infinite loop and, of course, how using rampant teleportation can enable you to solve puzzles involving crates of some kind. As they say, hilarity ensues.