At the time they were released, both Half-Life games, to some degree, led first-person shooters into new and somewhat unexpected directions.

While a few previous games had incorporated narrative elements successfully, Half-Life brought a sense of realism to its world with the use of simple non-combatant non-player characters and Half-Life 2 expanded on the believability of those NPCs and incorporated physics and environmental interaction to a greater degree than any other game of its time.

While the Half-Life 2 episodes have been able to extend Gordon Freeman's world and continue to make use of the once-innovative physics gameplay of the source engine and Portal pushed the use of the engine in impressive new ways, the series is still essentially rooted in linear level design and storytelling.

Now with even first-person games like Far Cry 2 and Crysis making use of the kind of open world  and non-linear, mission-based gameplay that has defined a whole genre of third person games like GTA and Mercenaries, is it possible for the Half-Life series to innovate in any way while still sticking to a linear style of gameplay and narrative? Is it possible to advance the story of Gordon Freeman in an open world or would that diminish the series as a whole?

I don't know what Valve has in store for Gordon Freeman and his associates in their long awaited sequel. I'm assuming new technologes like the gravity gun and portal gun will play a significant role. The people at Valve are incredibly talented and I feel like they will be able to do something big and new with the game's third installment, but I worry that by the time we get to the game's release, that a linear, first-person shooter will feel like a dinosaur.