Valve's got Half-Life down cold. And hey! That's okay 'cause we're not sick of it *yet*. But as good as HL is, how about something new? Honcho Gabe Newell hints at what they're kicking around at Valve:

You know, if you get two Valve people together, they're inventing new games. We're just sort of looking to find out how much we can design. God, I would love to work on a turn-based strategy game, personally. Maybe we'll get around to it, but not a lot of people would agree. But our ambitions have stripped our ability to ship by a couple of orders of packaging. But I'm sure there will be some doing new worlds, doing new game types. Hopefully, the flexibility we get by going for smaller projects will let us be more experimental rather than spending half a decade to come up with a whole project.

Well, whenever you figure that out, let us know. Because yes, we are looking forward to it.
Gabe Interview [Action Trip]