Development of the next Half-Life game

Development
Like other Half-Life 2 episodes, Episode Three will follow the adventures of Doctor Gordon Freeman. Parts of the episode will be set further 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 have neither been announced nor discussed by Valve to date. It has been stated that Episode 3 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 some distance away. The plot has been rumored to revolve around the Borealis - an ice-breaker vessel belonging to a rival corporation of Black Mesa, Aperture Science -- the same fictional company featured in the recently released Portal. It is believed some powerful technology exists on board. It would appear that the main objective of Episode Three is to find the ship and the technology on board and save Dr. Judith Mossman in the process. The various characters in the Half-Life universe have differing opinions about whether the technology on board should be destroyed to prevent another catastrophe or preserved to be used against the Combine, and hence it is likely that Gordon and Alyx will be tasked with one or the other over the course of the game, but most likely the first as Eli Vance was killed in Half-Life 2: Episode Two, and Isaac Kleiner is the character that supports harnessing the technology. It is presumed that the player also will see the G-man's plans for Gordon Freeman and Alyx Vance, and the "unforseen 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, but will most likely not occur seeing as the beginning of Half-Life 2 dashed whatever path the player choose at the end of Half-Life. Also that would leave the alternative option that the beginning of Half-Life 3 would establish to be non-canon and therefore irrelevant.

It is possible that the powerful technology could have to do with the destructive Artificial Intelligence GLaDOS, or the Portal Gun present in the game Portal. This is also supported by the back story of creating AI presented in Valve's viral marketing site http://www.aperturescience.com. This is also supported by Dr. Eli Vance stating that when the Borealis disappeared it took some of the dock with it, presuming that the technology on board is a kind of Portal Technology.