MegaMan 2 may perhaps be the best MegaMan ever crafted by the folks at Capcom. Now I know there are some people who prefer 3 or some of the X games over it, but that's not about that. I think 2 really is one of the finest sequels in the NES's library, and one of the few major sequels that was remotely similar to the original.
It may not have added many fancy new features that we saw in 3+, the X games, Battle Network, Legends, or any other MM game Capcom pukes out these days, but it did nail almost everything right. From the game-play, the difficulty, the platforming, and defiantly the bosses. They certainly weren't running out of ideas back then.
MegaMan 2 is a classic. No doubt in anyone's mind. If you haven't played one of Capcom's greatest gifts to gaming then you really should get yourself some sort of copy; because it's something not to be missed. You can see why Megaman 9 and 10 tried to take a much more simpler approach by playing Megaman 2.