Half life 2 Episode 3

For all those people who played Half life 1 or Half life 2 would have noticed that they were market changing games. Meaning that Half life 1 was the first game that was a first person shooter to be well received by consumers. When Half life 2 was released there was complete amazement and shock at how deep and interesting the storyline was. The graphics on both those games were completely unheard of at the time and even for a few years afterward.
Half life 2 episode 1 and 2 were released about a year apart. Valve used the Source engine for all of the games.
Although nothing much has been said about Half life 2 Episode 3, there are some things that valve have said to confirm that it is in existence and are working on it.
For instance, When Valve was questioned about Half Life 2 Episode 3 they did not deny that they were working on it.
Also Valve have recently stated that they will be learning Sign Language. They said that they would use this to explain why Dog and Alex can sign to each other and can "talk" to each other while no one else can understand what they are saying. This sounds like a interesting twist to the story.
I am very excited to see this latest installment for myself, and I hope that Valve will release early 2010. If it is anywhere near as awesome as any of the previous episodes I will definitely say well done to Valve.
Here is some concept art of how Half lIfe 2 Episode 3 will look.