5 - Mario Tennis (N64)
Long before The Great Mario Sports Whoring, there was only Mario Golf and Mario Tennis. Golf was a totally cool game in its own right, turning a yawnfest of a sport into an interesting video game, but it was Tennis that got people to give a crap about Nintendo sports. Everything just felt so tight and precise, from blasting a serve into the corner to incessantly volleying with three other players. Basically, it was a freakin' good tennis game that also happened to star Nintendo's biggest moneymaker. Later games added more to the menu, but perhaps a little too much crazy and not enough gameplay.
Accessible to newcomers yet deep enough for the hardcore, Mario Tennis was a fantastic follow-up to Golf. It's the first appearance of lame-o villain Waluigi and the first instance of a playable Birdo. You're also able to play as both Mario and Baby Mario, a feat we like to call "Paradox on the Other Side of the Net."
Also of note: this is technically the second Mario Tennis game. The first was a pack-in for the Virtual Boy.