I'm late to this party, so sorry if someone already said this, but:
Metroid
The first one was a huge turning point for videogames: The first game (in North America) to have a password system, one of the first 2D side-scrollers to... scroll? in both directions. Multiple endings depending on how well you did and the (then) huge surprise that Samus was a girl. Pretty sure that makes her the first badass chick protagonist in gaming.
Super Metroid is considered one of the greatest games ever made, containing a great blend of intense boss battles, tough gameplay in general (I HATE water...) and a great atmosphere created solely through 16-bit sound and not a second of dialogue.
Metroid Prime brought it to 3D, and even though most Metroid fans were worried how it would work out, it was amazing. When it was released, the graphics blew me away. I had to double check to make sure it was actually my Gamecube and not my Xbox that was running this game. The atmosphere in that game was up to Super Metroid standards, still without using dialogue.
Long story short, the first games created huge changes in video games as a whole. The later games built upon that legacy and while they didn't revolutionize games, they were still high quality games (not including Other M. That was just...ugh)
/Metroid fanboy gush