I too think that platformers peaked in the 2d phase. 3d ones, even my favorites still don't compare to classics like Super Mario World. But that's why i'm happy LBP is a 2d platformer. Maybe it can bring the genre back and do as good a job.
As far as killing Mario, even if this game is better than SMW I doubt it. He's been around far too long for an upstart like sackboy to tarnish his image in the least. Now if sony has a band of games to milk it like little big golf, tennis, etc then by the end of the generation he may have a sliver of a chance of starting to compete.
Not to mention he probably just can't get that huge until Sony does something bout the price of thier machine. $299 ps3 bundle with LBP would do both much better justice. Here's for hoping surprise holiday cut or more likely a new price point after this fiscal year has ended probably march or april when sales tend to go down anyway.