God, this is a hard question at this particular moment. Right now it's a toss-up between Sonic Mania, Final Fantasy XV, Horizon: Zero Dawn, Zelda: Breath of the Wild, and Kingdom Hearts III.
If I have to choose, though, it has to be Final Fantasy XV. Once that's out... I don't know how I could possibly choose between Sonic Mania and Breath of the Wild. Meanwhile, Kingdom Hearts III's release is still too far off for me to get overly hyped just yet.
It's great to see so many people answering FF XV, though I'm surprised since GAF as a whole seems to be so massively aligned against it just because it isn't Versus XIII. Are more rational minds finally prevailing?