Impossible choice again.
Between Prince of Persia, Sim City, Populous, Golden Axe and Xenon 2.
Prince of Persia blew my mind with the fluidity of the protagonist, it was magical to play and every death so gruesomely well animated. Prince of Persia peaked with The Sands of Time all though I really love the 2008 version as well. You can say it inspired Tomraider with it's brutal death sequences.
Sim City was a new genre for me and I spend countless hours creating cities and perfecting them. It got me into a long line of Sim City games as well as spinoff like SimEarth, SimAnt, SimFarm, SimCopter and I guess The Sims. Too bad online killed the franchise.
Populous is an amazing God game. I actually didn't play it until after I played Populous the beginning (another revolutionary game 1998) and the original was still just as mind blowing.
Golden Axe ran pretty well on DOS and was our go to 2 player game. We hardly ever made it to the end since we always turned on each other at some point.
Xenon 2 I played a lot. And it still ran on the old 8086 PC. It ran at half speed on that though which made it twice as long and a lot easier. I would play that while my dad was working on the 486. Trying different combinations of upgrades to get to the end.
I have to give the nod to Sim City as it definitely influenced my interest in maps, road planning and career choice into GPS navigation and street mapping. Plus I'm still interested in urban planning and recently made this poster to better understand what direction my County is going in to 2051.
Sim city in real life (County has to grow from 30K to 59K population over the next 30 years)