Ok, ok, calm down guys. I don't get the Prey / Portals! conversation. Prey has been in dev for a long ass time, they were talking about their 4D technology forever, it was the original vaporware. But that is neither here nor there, Portals! is an entirely different way of utilizing portal technology. In Prey, you had static portals that were used as an interesting means of travel. In Portals!, portals will be used as a means of everything, travel, movement, attacking, defending, etc. Why? Because they are dynamic. You can create a portal anywhere, you can even make an infinite loop. Portals! is the result of a small freeware/shareware group (whose names I don't have off the top of my head) that made a really cool game using portal technology, then Valve basically paid them to convert said game into the Source engine. The original game, I've read, was really fun, but very simple graphics. By combining it with the Source engine we get the best of both worlds.
This is a good thing, and a very unique experience.