Half-Life: Element 64

Half Life: Element 64 is a HL1 mod that is designed to feel like the a classic FPS, this is the official blurb:

"While CRT monitors, floopy disks and GSM cell phones are still hot, the world has to face an alien threat from dimension unknown. Black Mesa Research Facility is breached and only one man can save the human race from extinction. Step up to the task, load your shotgun and save the universe in this adventure inspired by classic first-person shooters of 1990s!"

https://store.steampowered.com/app/1625220/HalfLife_Element_64