I guess it just has to be about which games wowed me into playing more of that genre the most, that's the way a single game tends to have the most impact.

So I played every other FF game (except MMOs) because of FF7. Obviously the rest had to be fairly good themselves. But it was still hugely down to being blown away by 7 and needing more.

Ocarina of Time did the same with Zelda.

Fire Emblem Awakening did the same with SRPGs. Although in that case, very few are on the same level.