Topic. My guess is simplicity, which makes it easier for a majority people to play.
Personally, I have always been attracted to other platformers before turning an eye towards side scrolling Mario games. To this day, my favorite side scrolling Mario is Yoshi's Island, a game where you don't play as Mario at all. That game has varied level design, tons of different enemies, and best of all, varied boss fights. People often complain about how the boss fights in the NSMB games have little to no variety. In Yoshi's Island, I don't resort to the exact same tactics when fighting against Potted Ghost and Rafael the Raven. Unlike the koopalings where you just kind of jump on them three times and avoid the shell spinning (a couple of koopalings did the same run up the wall tactic in super Mario world too).
Then there is the Kirby series. Kirby does something different in almost every single one of his games to the point where you can't even define a traditional Kirby game. Kirby's copy abilities outnumber the amount of power ups that Mario can use, providing more options for your gameplay experience. Warioland games have a more defined style, but also provide you with a ton of power ups to use.
Yet none of these series have come close to rivaling Mario in terms of sales or fans. What causes Mario to have so much success over these other games?
THIS game? You mean THIS game we haven't even played yet? I'm not sure what you're asking really. Are you asking why Mario is more popular than other platformer series when you think it's inferior, or are you asking specifically why the NSMB games are more popular than other contemporary sidescrollers?
Sorry I wasn't clear. I'm asking about Mario. Not just this game specifically.
Brawl FC - 1332 8069 6690 http://i.imgur.com/OZ9aS.png
In all honesty, I found the levels in NSMBW to be incredibly varied. Seemed like every stage was based on a different environmental mechanic or power-up, even if the world themes themselves were familiar down to the order.
Plus, Mario just handles tighter than most other platformers. LBP is floatier and less responsive, for example.
The "bubble" mechanic counts for a lot, too. NSMBW introduced that, afaik, and it allows for even the most useless of teammates to keep from hindering the more seasoned players. This, combined with the fact that in NSMBW the screen scrolled ahead with the player who was in the lead, forcing the others to keep up. Much better than in some other games I've played where the screen scrolls with one player, who could potentially hold up the others; not trying to pick on LBP as I loved that game too, but having to wait for other players before the screen would move was pretty annoying, especially during times when they were using the team's lives trying to keep up. I think Kirby's Epic Yarn may have been the same way at certain points with the second player having to wait for Kirby, though my memory's more hazy on that one.
My SSBM combo vids: http://www.youtube.com/user/crowe1