Halo of course. I was skeptical until I played a demo, instantly bought in.

That's funny, I had this exact experience much more recently when Breath of the Wild was relatively new. I heard so many people raving about how good it was but I was never a huge Zelda guy. Went to Best Buy to window shop, they had a switch on display with BotW queued up. I don't think I even got in to combat before I thought, "ok, this is something special, I need to give this time". Still play it here and there when I'm bored of other games.