Here is a concise summary of the provided text:
**Half-Life Game Series Overview**
* **Development**: Half-Life (1998) was developed by Valve Software using the Gold Source engine, inspired by Stephen King's "The Mist" and the video game "Doom".
* **Gameplay & Story**: The series follows protagonist Gordon Freeman through a scientific world with a compelling storyline, initially focusing on an incident at Black Mesa research facility.
* **Interesting Facts**:
+ The game's name "Half-Life" refers to a scientific term from nuclear physics.
+ The original Gordon Freeman character model was called "Ivan the Space Biker".
+ The German version of the first game had significant censorship changes.
+ A Japan-exclusive arcade game, "Half-Life 2: Survivor", was released in 2006.
* **Unfinished Business**:
+ Half-Life 2: Episode 3 (or Half-Life 3) has been in development limbo since 2007.
+ A cancelled episode, "Return to Ravenholm", was being developed by Arkane Studios in 2006-2007.
* **Series Storyline Recap**: The narrative spans an alien invasion, the Combine Empire's takeover of Earth, and Gordon Freeman's key role in the rebellion, leaving off with an unresolved cliffhanger awaiting Episode 3 or Half-Life 3.
Here are the key facts extracted from the text, each with a number and in short sentences, excluding opinions:
**Game Development & Release**
1. Half-Life was developed and released by Valve Software in 1998.
2. The game was created using a heavily modified version of the Quake engine, called the Gold Source.
3. Half-Life was initially planned for release in late 1997 but was delayed after Valve decided to remake the entire game.
4. The remake delayed the release by almost a year, with the game finally coming out in November 1998.
**Inspiration & Name Origin**
5. Early inspirations for Half-Life included Stephen King's "The Mist" and the video game "Doom".
6. The term "Half-Life" is a scientific term used to determine the time required for a specific property to decrease by half.
7. The term is commonly used in the context of nuclear physics and nuclear chemistry.
**Gameplay & Characters**
8. The German version of the first Half-Life has significant changes, including no blood when shooting enemies.
9. In the German version, killing allies results in them sitting down and shaking their heads instead of dying.
10. Marines in the German version are replaced with robots.
11. The character model for Gordon Freeman was initially used for another character, Barney, in Half-Life: Blueshift.
**Gordon Freeman's Character Development**
12. Gordon Freeman was not always known by his final name; Valve employees initially called him "Ivan the Space Biker".
13. Gordon Freeman's character design went through several versions, including different glasses, suits, and hairstyles.
14. In the first game, Gordon Freeman had a ponytail, which was later removed in Half-Life 2 and subsequent artwork.
**Other Games in the Series & Related Titles**
15. An arcade game, Half-Life 2: Survivor, was released in Japan in 2006, based on Half-Life 2.
16. Half-Life 2: Episode 4, codenamed "Return to Ravenholm", was in development by Arkane Studios but was canceled by Valve.
17. The cancellation was due to the market being oversaturated with zombie-related titles at the time.
**Storyline & Universe**
18. The Combine Empire is a powerful, intergalactic organization in the Half-Life universe.
19. The Combine invaded the Vortigaunt's homeworld before the events of Half-Life, leading to the Vortigaunts' escape to the border world Xen.
20. Scientists at Black Mesa were experimenting with teleportation technology, leading to the Resonance Cascade (Black Mesa Incident).
21. The G-Man orchestrated the Resonance Cascade, forming a portal between Black Mesa and Xen.
22. The Vortigaunts invaded Earth through this portal, using their minions and enslaved species.
23. Gordon Freeman fought off the alien invaders and eventually defeated Nihilanth at the end of Half-Life.
24. The G-Man was impressed by Freeman and offered him an ultimatum: work for him or die.
25. The Combine invaded Earth after the events of Half-Life, reducing the population and enslaving humanity.