If you ask someone for a list of the best platformers of the 8-bit era, or really, best platformers of all time, Mega Man II [App Store] will undoubtedly be on that list somewhere and likely near the top. Mega Man II had it all-- Highly refined controls, an excellent difficulty curve, and a significant improvement on the then-revolutionary system seen in the first Mega Man that allowed players to harness the abilities of bosses.
The original release of the Mega Man II port for the iPhone was plagued with controls that made the game nearly unplayable. Also instead of porting the original NES game, Capcom ported the version that had been retuned for cell phones, making the game significantly easier.
After hearing the cries of countless disappointed gamers, Capcom revisited Mega Man II and released the significant 1.5 update. The first improvement made is the inclusion of "Classic Mode". Once enabled, Mega Man II plays much more similar to the original version of the game, but sadly, most of the control problems still persist.
In addition to the terrible portrait mode virtual joystick controls seen in the original, Capcom added an optional landscape control method that can be toggled by turning your iPhone to the side, or by locking the game in to landscape mode in the options. This secondary control method is significantly better than the first, but still due to the limitations of virtual buttons on the touch screen it is extremely difficult to jump and shoot at the same time.
However, the addition of this new control method at least elevates Mega Man II in to the realm of playability. It's now possible to make it through a few of the easier levels, but I still have no idea how given the current control scheme of the game you would ever make it through Dr. Wiley's castle.
Thankfully, Capcom recently released Mega Man II Lite [App Store] which will allow fellow nostalgic gamers the ability to sample the control schemes before deciding to shell out the $4.99 for the full game.
Until Capcom can figure out how to further improve the controls, I would still recommend sticking with any of the other Mega Man II ports that exist on nearly every other platform. In the meantime, if you're looking to take care of some Mega Man nostalgia, there is a ton of great fan-made Mega Man-inspired music on YouTube between The Protomen and Brentalfloss as well as a huge catalog of remixes on Overclocked Remix.