not exactly a hidden gem, because it’s quite popular, but beneath a steel sky!

Bit hard to narrow it down.... what do you enjoy? And have you played much from that era?

Just off the top of my head... simcity 2000, Ultima 4,5,6,7, the quest for glory series, civilization 1 and 2, fallout 1 and 2, xcom, master of orion.... there are a ton of classics that are still worth playing.

For something perhaps a little less popular, maybe try Tex Murphy?

Edit: oh, I just remembered Commandos! if you're a masochist, anyway. That game is hard as balls. Fun, though.

Tyrian 2000 is an easy choice given it's permanently free on GOG. It's a really fun old shmup with story and arcade modes, lots of difficulty settings (look up cheat codes if you need to make it harder) and a pretty solid amount of weapon customization. Still very much holds up today.

Personal favorite from the era: X-Wing! There were plenty of better Star Wars flights sims in the years after it, but the original on floppy disks holds a special place in my heart.

I'd say Duke Nukem, include Duke Nukem 3D, but those don't seem to be on GoG.