I want to enter the world of metal; help me find a gateway genre?

Thrash Metal. Listen to Anthrax, Megadeth, Death Angel, Testament, Metallica, Overkill, Slayer, Nuclear Assault, Xentrix, Evildead, Exodus, Flotsam & Jetsam. Those are good bands to start with but there are so many other great ones as well that you will discover as you listen. Enjoy