While it can't always be said that western cover artwork is superior to that seen in Japan, it's important to remember that for many gamers growing up during the 8 and 16-bit eras, it was all they knew - and for that reason alone it's easy to see why so many Nintendo fans might have a nostalgic connection with the (often inferior) cover art in question.
Mega Man is a series which has endured a rather storied history when it comes to western artwork - the North America cover for the first game has gone down as one of the worst examples ever. However, as the sequels rolled by the quality thankfully headed in the right direction, giving us several striking and memorable boxes to stare at longingly as we tried to make up our minds about which one to buy with our precious pocket money.
Nintendo Age forum member Buyatari is such a fan of these western Mega Man covers than he has assembled quite a collection of original artwork. These are the actual paintings created by artist Greg Winters (who would also do work for Sega during the same period) which were used on the boxes, and the fact that Buyatari has been able to obtain so many of them is really impressive.