I'm a pretty big fan of these sets and I really like the direction that K'Nex is heading with the line in general. Though the main bulk of the series is all about the Kart racing, and it's all pretty cool stuff all by itself, I'm perhaps most optimistic about the stand alone figure line that you see pictured to the left.
There is no (and really never has been a) Super Mario Bros. line of toys. Glimpses here and there over the years of small figurines, models, and mystery boxes have teased fans- but there's a real dearth of real action figures in a continuing and a total lack of playsets. For a property that's been around as long and is as popular as Mario Bros is, that's a straight-up crime. I mean, there's really nothing out there that represents a full and fleshed out menagerie of characters from the games.
As for the line as it stands today- there's plenty of awesome stuff coming in 2012. More bikes, karts, courses and even motorized vehicles (!) are all on the way. Some of the new additions to the courses are worth getting excited about too. There are a lot more power-ups and course specific enemies making there way into the sets. Shy-Guys alone warrant quite a bit of enthusiasm... well, they do from me anyway. Now, about that 'World 1-1' set...