The Mega Man X series is the perfect successor to its parent series because it was able to improve on already established elements (like sliding, hidden items, stage design, etc) and innovate them to generally positive results. Sliding became dashing, hidden items became upgrades to your life, health and/or firepower while stage design changed in a way that the player was able to interact with it more. The story also began to take a more active role in the way each game played out, with various antagonists such as Vile or the X Hunters harboring their own motivations that made them feel more complex (admittedly not much) than Dr. Wily's take over the world schemes. Even Sigma, the recurring boss of each game, started his descent into evil with a rebellion instead of a plan to subdue the world - though he did fall into the latter category in later games. While other components of the X series received mixed to negative reception in later installments, such as the shoddy level design in 6 or the slowed down gameplay in 5, X1-3 represent the best of what the franchise has to offer in regards to these elements. The gameplay is fast, furious and tight. X4 is also great, but the standards it holds are different - the story of Zero seems more to be the emphasis in this one, with the framework of the game changing just a bit. Dashing becomes slower and the fact that you can choose from two different characters allows the player to tackle the game in separate styles. X5 and 6 are generally considered to be bad, but even I think that they have redeeming qualities. It's better for you to play these and form your own opinions rather than taking my word for it; just know that 5 will be slower and MUCH more linear, while 6 will have downright stupid level elements that will provide you with a legitimately unfair challenge. Still, you may enjoy them. You'll probably find yourself going back to 1-3 the most, though.