It really depends. I've heard that Nintendo wanted something as breakthrough as the first, so they wanted a game that scrolled up and down. I believe that Doki Doki Panic was originally going to be Super Mario Bros. 2 but Nintendo decided to stick with the original format in Japan worried that it was too much of a departure. Here's a video about it from Did You Know Gaming. I don't know what their source is, but I tend to trust them. Skip ahead to about 3:50 to get to the part about Mario 2. Personally, I love Mario 2. It was a lot of fun even though it was so different. Having the Lost Levels, I must say I prefer the version one got. And it has nothing to do with the difficulty.