all games are not created equal

Since MM9 was intended to be very much the same as MM2, I feel that this is a very fitting comparison.

MM2 is not nearly as hard as MM9.  Not even close.  MM9 has to be one of the hardest NES games I've ever played.  There were parts that I had to play over and over again for at least an hour in order to finally beat it, and I would consider myself pretty good at games.  If you like the challenge, MM9 will definitely give it to you.

MM9 adds a couple sweet features, like the ability to buy and use items and various achievements that you can earn in game.  MM2 let you use power containers, but that was it.

The one place where MM9 really loses is the music.  MM2 had the most memorable music and I still love the songs from that game.  MM9, while it did have the same feel as the usual Mega Man music, just didn't have those catchy hooks and memorable tunes.

MM2 wins out because it's a game that can be enjoyed by a larger group of people and not just the hardcore Mega Man fans.  MM9 kinda requires you to really love Mega Man, otherwise, you would never even bother with trying to beat the game because of how insanely difficult it is.