- Breakthrough Hit: This game put Valve Software on the map as one of the premiere game studios.
- Dueling Works: More or less in direct competition with Si N, which came out two weeks earlier, and Blood II: The Chosen, which came out the day after. Neither of them really stood a chance.
- Fan Nickname:
- One of the rooms early on in the original game contains several cargo crates suspended over what appears to be a bottomless pit. Thanks to Freeman's Mind, it has become known to some as the box-smashing room.
- Fans often call the Gonarch "The Gonad", for... obvious reasons.
- Shout-Out: To AKIRA, of all things.
- Vaporware: A Mac (that is classic Mac OS, not Mac OS X) version was planned, developed, and close to releasing in 1999 when Valve suddenly pulled the plug. A Mac version wouldn't see release until an OS X port was released in 2013, but it most likely uses none of the code from the original port attempt.
- What Could Have Been: Not as infamous as its sequel in this regard, but nevertheless the game went through a significant number of changes before release.
- It was originally planned that the Scientists and Security Guards would be hostile toward Gordon, believing him to be responsible for causing the incident. But AI tests that had the guards following the player and fighting other enemies greatly appealed to playtesters, and Valve realized they were much more interesting as friendly NPC's.
- Many enemies were cut from the game. Among them were a minigun-wielding Human Sergeant and a Xen enemy dubbed "Mr. Friendly", who would be able to knock off Freeman's glasses and cause his vision to go blurred, which was considered an impressive effect for back then, but cut for being annoying. Also, it would kill Freeman by raping him.
- Dr. Gina Cross was, at one point, intended to be Gordon's spouse and a playable character, with the player choosing between her or Gordon at the start of the game. The character you didn't choose would be an NPC you would encounter and interact with throughout the game, but Valve considered the idea unfeasible at the time and Gina was recycled into the holographic instructor for the Hazard Course, then later became a playable character in Decay.
- Cut voice lines exist for the HEV suit announcing the acquisition of new weapons. Interestingly, these sound files indicate that the .357 Magnum was originally a .44 Magnum instead.note Another cut voice line refers to the Tau Cannon as a "hypervelocity projectile weapon", suggesting it was originally planned to be akin to a railgun instead of an energy weapon.note
- A number of characters went through redesigns. Gordon's original design originally had a wild, unkempt beard and thicker face going along with a much larger HEV suit that that led to him being dubbed "Ivan the Space Biker". This was refined into a trim goatee and a more form-fitting suit for the final design. Scientists and Security Guards had much more exaggerated and cartoonish faces before being toned down into something more believable. Female scientists were planned, with a story bit involving one betraying Gordon and sending soldiers after him. They were cut due to memory limitations, though the base idea would later be realized in Half-Life 2 with Dr. Mossman - who, in a Mythology Gag, presents herself as a rival to Gordon who he never knew existed.
- A port for the Dreamcast was in development by Gearbox and actually finished (trailers advertising the port came out a few months before launch), but it was cancelled just weeks before it was supposed to come out due to the publisher, Sierra On-Line, not being pleased with the Dreamcast's sales numbers. The expansion pack Blue Shift and the High-Definition pack included within it were originally meant to be exclusive to the Dreamcast port, with both being repurposed for the PC after its cancellation. The Dreamcast port was eventually leaked online years later and found to be fully functional, if awkward due to the limitations of the Dreamcast's controller, and fans later released the Dreamcast port as a mod for the PC version of the game.
- Valve planned a number of multiplayer gamemodes beyond deathmatch, but were forced to cut them due to time constraints. This video shows remnants of a cut cooperative mode left in the "Subtransit" multiplayer map. A cooperative mode would finally be realized with Half-Life: Decay.
- Apparently, in Half-Life: Decay, there would be some sort of scene where Gina and Colette would have to save Freeman after he was captured in the main game, explaining why the soldiers didn't just kill Freeman by shooting him or anything when they captured him.
- Working Title: Quiver, which is a double Shout-Out to The Mistnote and Quake.note
Trivia / Half-Life