The first game I remember truly getting into was a third-person shooter on the PlayStation 1 called Army Men: Sarge's Heroes 2. (I would've played SH1 first, but considering I was maybe five years old at the time...)
You're a green plastic soldier leading a squad of characters, fighting a giant army of tan soldiers. I don't remember a ton about the game, other than its mix of environments the soldiers fit right into, and "real-world" locations where they're tiny toys battling over beds and bathtubs.
This very day, somewhere lies my big plastic box of little plastic soldiers that I'd play with all the time. That game got my parents to buy a lot of molded plastic.