Three years ago, I was considering buying a Zelda game (for the first time). Then I saw that Pokémon ORAS owners could get a free game in the eShop. I chose A Link Between Worlds. It's still my absolute favorite video game.
I also could have bought the Metroid Prime Trilogy for £3 two years ago, but I didn't because I don't like the Wii. Now I kind of regret that.