Well, I honestly don't know where to start. There are many reasons as to why I got into the Oddworld series. I, for one, am a female gamer-I love to play games, so I know quite a bit about them, and I can honestly say that there was something fresh and new about Oddworld that caught my eye once I began to play it for the first time. For one thing, the series is very story-driven. Back in 1997 (Or any time, really.), I had never played a game about a meat-packing slave that had everyone after him and was trying to free his people all at the same time-that whole idea was something new to me because the gaming industry is based on first person shooters (with or without a story), for the most part. Many Americans are hooked on this genre, (especially the male gamers.) Also, the characters, while not cute or even attractive physically, are very attractive when it comes to their personalities-these characters actually appeal to me because of their personalities and to me, they are very realistic and not the typical run-of-the-mill hero saves the universe/evil villain trying to take over the universe. They are believable. They are brought out as individuals with feelings and interests- not just characters, but people. I believe this is one of the major reasons why this series has such a large female fanbase. Take the old school video games such as Super Mario Brothers, for instance. While this classic series, I must admit, is very addictive, exciting and fun to play, it barely has a story or plot, and the characters seem to lack emotion and personality (In the old school games, I don't play the new school Mario games much, so I can't judge those.). Oddworld, on the other hand, brought something new with everything-from the characters to the fresh, stealth/platformer gameplay. This series is truly a work of art.
As for sales numbers, I don't exactly know about those-I can never seem to find what they are, so I'm terribly sorry that I can't give you any info on that.
I hope I have helped in some way, though.