Despite the fact that there have been no new Mega Man X titles since 2004, the series is still very much alive in gaming's collective consciousness. The Mega Man X Collection and Mega Man Maverick Hunter X (a comprehensively-redesigned version of Mega Man X) came out in 2006. Even as late as 2011, fan-favorite Zero has shown up in mega-hit Marvel vs. Capcom 3. A simple Google search for "Mega Man X" reveals a slew of fan sites with a thriving online community, while YouTube teems with "Let's Play" videos and remixed music tracks.
Mega Man X had three installments on the SNES that were everything a kid could have hoped for in those days, and because of their bloodless violence and instantly-recognizable protagonist they were an easy sell for parents. They provided an extremely challenging experience, but any kid with enough patience could triumph over the sinister Mavericks and their machinations. A password save system meant that players would never lose their progress (at least until their mothers threw out their meticulously-maintained Post-It password repositories), Sub Tanks could restore health during even the toughest boss fights, and every enemy, including the final boss, had an easily-discoverable weakness to certain weapons. In short, the games were tough enough to keep kids busy for a long time, while still allowing for victory in a time before GameFAQs.
The second and third installments built on the success of the first one, refining the formula instead of reinventing it. Mega Man X2 added an optional item-hunt that added three very challenging bosses and changed the final cutscene considerably if completed. Mega Man X3 went even further, adding a second set of armor upgrades, three optional bosses that had to be defeated with special weapon combinations, and the fan-favorite Zero as a playable character. Depending on how a player used Zero, the game even offered multiple endings (and a spicy "damn" that managed to sneak its way into a K-A rated game).
One of the reasons the Mega Man X series gained popularity was its relatively elaborate storyline. The plot is not deep and the narrative is not especially compelling, but Mega Man X provided a much more involved story than its NES predecessors. Gone was the world of the original Mega Man, where the nefarious Dr. Wily created robots with the intent of doing mischief. Sigma and his contingent of Mavericks viewed themselves as freedom fighters: the Mavericks were evil due to an omnipresent virus, not any particular intent to do harm. Since X, Zero, and Sigma could think, feel, and reason, their intertwining stories seldom told straightforward tales of good against evil. In Mega Man X2, Sigma's death failed to make a dent in the Maverick population and in X3, a good Reploid ended up committing unspeakable evil by buying into Sigma's desire to create a utopia where Reploids could live apart from humans. The stories were darker and dealt with mature themes like free will, sacrifice, and pacifism.