Capcom has released Mega Man X for the iPhone and iPod Touch, but unfortunately not the iPad. It's a remake of the original Mega Man X on SNES, but the retro feel you were hoping for isn't entirely here as the graphics have been completely overhauled and the company has added an "Easy" mode for those who aren't used to having their right arm replaced by a blaster. Capcom has also added in-app purchases for nearly every upgrade you'd normally have to claw your ways towards in the game, including a "Complete Set" option for $3.99. There's also several "cheat" modes like auto-fire.
You can still play the game in normal mode, but even so, the changes aren't making the Mega Man fanbase very happy. If you're not a purist, however, it can be had in the App Store for $4.99 in all regions. If you are a retro gaming purist looking to get your fix on iOS, may we suggest a little Chrono Trigger?