My first incremental "game" would have been Progress Quest, probably. I really liked the idea of numbers going up, and there were a few early clickers about in 2009, 2010 - and then I found Anti Idle - which I still play today. Have played everything on the Ultimate List of Incremental Games, and since then the market's been flooded with low-effort reskins and I lost interest in keeping up and shoot for more satisfying games rather than a broad spectrum.
My favourite game for years was Civ IV, which I see now I played in a sort of incremental-ish fashion - for those who know it, I played using cultural victory only, no space, city flipping through culture, no wars. My victory objective was to win through supreme culture and incrementally take all my opponents' cities that way. It was always interesting trying to place the big culture-generators at the periphery of my empire for best effect. This would have been late-90s? I've still never won the game this way, but lots of incrementals have no end :D