I'm not too much of an impulse buyer, so I don't buy very many games I've never heard of. If a game I've never seen before looks really interesting, I generally read a little about it online before buying it. However, back when I was still renting games regularly (before all the best video rental places stopped carrying games for some reason), I would frequently rent ones I'd never heard of.
There was this little SNES game called On The Ball that I one day rented without knowing anything about it because back when I was little I was obsessed with spheres for some reason. I wound up loving it.
Same with Bust-a-Move '99, a game that I rented and was hooked on, and I still have no idea why. Although I don't own it, I still make a beeline for that one every video game night.
I had heard about the Harvest Moon series but had never played any of the games, and since there were so few copies I had no clue how to get one, then when browsing through a vintage game store I found Harvest Moon 64.