Yeah... Megaman X is to Megaman the first as an...
Mario 64 is to SMB
M16 is to a colt .45
Zelda OOT is to Zelda 1
Maroon is to hot pink
PSP is to DS
WoW is to the original warcraft
WoW is to Guild Wars
Dr. Pepper is to Mr. Pibb
Getting laid is to jacking off to the bra pics in the Sear's catalog
Megaman X is arguably the best Megaman ever... Yes, it's the same principal. Like Mario or LoZ, it has been rehashed with similar mechanics and ideas, but at the same time delivering neverending joy for those interested in the series.
Yes, you run and you shoot from the side... You collect weapons, battle bosses, etc., like you would with any other. But just about everything in it was just sooooo good compared to everything else, and the goodness was original... I don't get into megaman much now, but from what I understand there hasn't been much in the way of improvements.
Sometimes, series reach an apex, then go downhill... It's rather common, actually... OOT > WW, Megaman X > the latest... just to name a couple
And what's great about the above games is that you can play their BEST games in the series, then go play the older ones and not have anything lost from the experience.
.... Yeah, I just realized I sort of rambled on there, but simply put: Megaman X, while it does the same thing as the others, is simply better because of the presentation and the actual gameplay... Like with OOT, it looks and plays in such a much better/different/immersive way than Zelda 1 or 3.
Play Megaman on NES, then play Megaman X on SNES... you'll see what I mean.