Since I have only played a few of the Metroid games to completion, I'll compare Mother Brain on the original Metroid to the version on Super Metroid. Truthfully, I don't think either one of them was particularly hard. Super Metroid was a much harder game then the original, but I would have to say the original has a harder Mother Brain. My primary reason for saying that is the frustration factor. When you're trying to blast Mother Brain on the original, you end up getting knocked into the lava. Consequently, you start getting frustrated, then you start playing worse. On Super Metroid, the same thing happened, however, I don't think it was as prominent. What do you guys think is the Metroid with the hardest Mother Brain?