I'm aging myself here.
The first game I really played (aside from my granddads super old Pong console) was Sonic the Hedgehog on my Sega Master System II.
Don't remember much of it, but I know this: I never played a Sonic game since. I guess it just wasn't for me.
What about you?
ZX81. Various games I don't remember, the one that always sticks in my mind is Forty Niner which we needed a 16K RAM pack for. We also had an Acetronic which predated the ZX81, although I think I may have used the ZX81 first (not entirely sure). Both were part of my early gaming journey.