I feel like there wasn't really a single golden age for PC gaming, since each genre has had its own golden age. Doom, Duke Nukem, Unreal, and others probably comprised the first FPS Golden Age, but that was happening separately from other Golden Ages that were happening. You also had RTS games, Strategy games, and a bunch of other PC genres.

As far as when that first FPS golden age ended? I'd almost say that 1997's Goldeneye 007 for the N64 marked the "end" of the PC FPS golden age, since that's when console gaming got its first big exclusive FPS hit. EVERYBODY I knew was playing that game when it came out and you just couldn't play it on the PC at that time, it marked a shift from PC to console gaming. Some genres would never make the jump successfully, like RTS games, but FPS games and Adventure games seemed to work well and that's where all the cool new games went to. Obviously consoles had had hits before this, but that seemed like the first time they got something above and beyond just Mario or Sonic-style platformers.

Personally, I think the first golden age ended with the decline of the shareware model that was used by many of the classics in the nineties.

Sure, it wasn't the decline of shareware that ended it, but de decline of the model went hand in hand with the rising cost of development and longer development timeframes that ended the games boom of the nineties.

That's my take at least. Might just be an old man with rose tinted (shareware) glasses.

Golden Horse Armor. That's when it ended.

TES: Oblivion, FC3, Minecraft - all formed the landscape in one way or another in the days I was consumed by this medium. I don't think I can draw a line here. It always seemed like a powerful stream of water where some deviations created their own whirpools in a race to reach this ideal product for sale.

In my head? Half Life 2 was the beginning of the end for that era. Maybe not exactly at that point but it was a great game that brought even more people to steam than ever before. From there we now had a centralized marketplace for games with a massive audience and we start seeing the creeping corporate influence of "microtransactions", the death of the expansion and introduction of dlc story content, beloved franchises abandoning originality in the pursuit of mass market appeal. That kinda thing. Of course if not half life 2 then it would be the Elder Scrolls Oblivion, who truly started something horrible with their horse armor dlc.

The future is largely Indies or AA games, everything else is going the way of call of duty at this rate.

What exactly makes now not the golden age? There are more games than ever and emulation tools, the Steam deck, big modding scenes, etc.

i think to a degree implementations of services like Games for Windows Live stopped the first golden age for larger studio type games. ofc not all games were GFW but such a service that after its cancellation caused some games to just become unplayable on PC was wild.

When Gol D. Roger died