It's all been leading up to this.
Put me in front of Mega Man X and I will play it and probably beat it. The game is so familiar to me now that any playthrough is about 80% muscle memory, and that's okay, because the other 20% of my thought process is something like "this is so awesome." Mega Man X came out around the same time as Mega Man 7, and it was instantly clear which series was going to be the big deal. X took the classic Mega Man stage progression and boss weapon weakness mechanic and layered new moves, new upgrades, the ability to revisit stages and lots of exploration and experimentation to the formula.
Mega Man X travels through eight various environments to defeat eight animal-like Robot Masters before taking on his old mentor (who's gone rogue, er, Maverick), Sigma...and his dog. X must find Heart Tanks, which increase his life bar, Energy Capsules which refill his life bar (and must be recharged) and new parts from his long-dead creator, Dr. Light, if he has any chance of beating Sigma. The game is essentially flawless, with amazing music and big, beautiful sprites. The goofy, friendly aesthetic of the old Mega Man series is gone--Mega Man X is for real.
While subsequent games in the series are also rock-solid, nothing quite reaches the level of zen that the original Mega Man X does, and if you've never played it, I envy you! To play Mega Man X for the first time would be a real treat. If you've played it already, you know how good it is, and you've probably already bought it. If you haven't, what's wrong with you?