Development of the next Half-Life game

Development
Like other Half-Life 2 episodes, Episode Three will follow the adventures of Doctor Gordon Freeman and Alyx Vance. Parts of the episode will likely be set farther north, possibly in arctic conditions. Valve has said that they intend for each episode to highlight a major new feature or gameplay design element. In Episode One, this was the interaction with a well developed NPC, along with full implementation of the Source High dynamic range rendering (HDR) lighting system. In Episode Two, this was creating large outdoor environments, battles previously unseen in the Source engine, performance and rendering enhancements to the Source engine to accommodate multi-core processor architecture and a new cinematic physics system to create large physics-based events. The new gameplay and Source engine features for Episode Three, but this episode will possibly be out in March of 2009. It has been stated that Episode Three will be the final Half-Life 2 episode, but not the end of the Half-Life series.

Plot
The plot of Episode Three is largely unknown. Judging from events at the end of Episode Two, it will see Gordon Freeman and Alyx Vance moving even further away from City 17 to an arctic setting. The plot is expected to revolve around the Borealis - an ice-breaker vessel belonging to a former rival of Black Mesa, Aperture Science -- the same fictional company featured in Portal. It is implied that some powerful technology exists on board and the main objective of Episode Three will be to find the ship and the technology on board whilst rescuing Dr. Judith Mossman in the process. The action to be taken is unclear as the two characters in the Half-Life universe that have expressed opinions on the matter disagree about whether the technology on board should be destroyed to prevent another catastrophe or retrieved for use against the Combine. Eli Vance was killed in Half-Life 2: Episode Two, so it is unclear about who is leading the resistance but it seems likely that Isaac Kleiner would take on that role and he believed harnessing the technology would be the best course of action. This is not a guarantee though as Eli's death may change his mind; in either case, Alyx may wish to honor her father's last direction to destroy it.

It is anticipated that the player will see a glimpse of the G-Man's overarching plan for Gordon Freeman and Alyx Vance, as well as the "unforeseen consequences". It is also possible that, being the final episode, there may be a function of player choice towards the end that affects the outcome; however, like Half-Life's ending, only one of the choices will end up as canon in Half-Life 3 if Valve proceeds in the same way.

The fate of several characters in the game may also be revealed. It is not known whether Judith Mossman is still alive after being tracked down by Combine forces and as she was the subject of Gordon and Alyx's journey northward it is presumed her fate will be revealed. Barney Calhoun's absence from Episode Two may also be explained, though it is unknown whether he will re-appear in the third episode. The overall status of Dr.Breen is also ambigious, as though his appearances are minor in Episode One and Two (especially a brief moment in the latter), they are still significantly present and his fate is ultimately unclear.

The technology in question is most probably a form of portal technology similar to that which allowed the Nihilanth and later the Combine to invade, as well as in Half-Life 2 which featured the Citadel's destruction creating a super portal. If the pattern continues to repeat, the Aperture Science technology will likely be a highly efficient and accurate form of portal like the Portal Gun but capable of moving much larger objects than an individual person, such as a whole ship (and part of its drydock). The Borealis ' teleportation shares many similarities to the urban legend of the Philadelphia Experiment in which the USS Eldridge was rumored to have been rendered invisible by experimental technology, and in some versions of the story the ship had accidentally teleported from it's dry dock to a U.S. naval base over 200 miles away. And in the most radical versions of the story, the ship achieved accidental time travel.

Characters
Gordon Freeman and Alyx Vance will of course be featured. The inclusion of any other characters is unknown, though more are likely, such as Dr. Kleiner and Arne Magnusson.Adrian Shephard may make an appearance, as valve has stated that they would like to return to him.

Enemies
Advisors are known to be encountered, though most details are unknown until more information is released or leaked, however, it can be reasonably assumed that most of the existing Combine units like the Combine Soldiers and Hunters will be encountered, especially since they were seen in Mossman's video.

Also, not a single Half-Life game yet has lacked Headcrabs, Zombies, or Barnacles, so they are likely to make appearances.

Enemies seen, but not encountered in Episode Two such as City Scanners and Gunships could possibly have an appearance.