You should know the plot to Half-Life 2. If you don't then go play it.
It would be a 6 movie saga. Directed by Kevin Smith and Produced by J.J. Abrams.
"Half-Life 2: Red Letter Day" would begin in 'Point Insertion' with The G-Man's Speech and End in 'Black Mesa East' with Freeman Entering Ravenholm.
"Half-Life 2: Ravenholm" would all take place in 'We Don't go to Ravenholm' ending in the mines
"Half-Life 2: Nova Prospect" would start in 'Highway 17' with Freeman leaving Ravenholm and end in 'Entanglement' with Freeman teleporting and a white light.
"Half-Life 2: Our Benefactors" would start in 'Anti-Citizen One' with Freeman teleporting to Kleiner's lab two weeks later and end in 'Dark Energy' with The G-Man's farewell speech.
"Half-Life 2: Undue Alarm" would be 'Episode 1'
"Half-Life 2: Our Mutual Fiend" would be 'Episode 2'
Now for the Cast
Joel Edgerton as Dr. Gordan Freeman
Hugh Laurie is too old to play Freeman. Freeman is in his 30's.
Rosario Dawson as Alyx Vance
Kyle Chandler as Barney Calhoun
Michelle Forbes as Dr Judith Mossman
They used her voice and face for the character. She is the best possible choice and she can act.
Morgan Freeman as Dr Eli Vance
Colm Feore as Dr Isaac Kleiner
Ian Holm as Dr Arne Magnusson
This character would have a bigger role.
Malcolm McDowell as Dr Wallace Breen
I am President John Henry Eden and welcome to City 17, it's safer here.
Ted Levine as Colonel Odessa Cubbage
Jean Reno as Father Grigori
Tony Todd as the voice of the Vortigaunts
He did the voice in the games.
Simon Pegg and Nick Frost as Griggs and Sheckly
AND
Steve Buscemi as The G-Man
Wake up and smell the ashes.
-Later