Casting Gag: Darth Vaders voiced by Matt Sloan, who played him in the web comedy Chad Vader. This is even Lamp Shaded in an achievement/trophy unlocked by killing 12 stormtroopers called "Worst Day-Shift Manager Ever," referencing Vader's job in the aforementioned comedy.
Development Gag: Galen Marek's code name "Starkiller" was Luke's surname in the prototypical Star Wars; which George Lucas changed at the last minute.
Franchise Killer: The second game's disappointing numbers (combined with the closing of LucasArts three years later in 2013 and the halting of any new material for the Legends continuity on new owner Disney's orders) killed the possibility of a third game, and Starkiller's adventures were Left Hanging.
Let's Play: The voice actors that played Starkiller and PROXY did a series of Twitch streams where they played through the game while talking to the developers about how The Force Unleashed. As of writing, it has yet to be finished.
Novelization First: The respective novels for both games came out before each game was released.
PROXY would have been a "Corpse droid" where he often harvested organs to complete himself. However, because of his not fitting in with the team dynamic, and more obviously because the only way to give a comical aspect to him (grafting organs into himself) was considered too gruesome for what was intended to be a "T" rated game, he was redesigned to be a holodroid.
Before creating the character of Rahm Kota, the makers wanted Starkiller's Jedi mentor to be the Force Ghost of either Qui-Gon Jinn or a reformed Darth Plagueis.
Starkiller could have been called "Darth Icky" or "Darth Insanius" via official mandate from George Lucas. No, really.
Had Star Wars The Force Unleashed III not been canceled, it would have Starkiller team up with his former master Darth Vader against a new threat by Emperor Palpatine.