It's a good game, way easier than 'normal' MNR story mode but a lot of fun to both race and create with.
However, whilst many of the track-construction tools and opportunities are very good, the lack of true, full kart customisation is a bit of a letdown. Sure you can make some really decent custom karts, but the lack of an object point editor means that you're working pretty much with just stock parts or the limits of Boolean modelling - ie using one shape to add or subtract from another - whereas even LBP1 let you fine-tune the shape of parts you made (and let you scale them down much further)
The sticker functionality is also annoyingly 'dumb' compared to the extensive tool-set in MNR, (but I'm guessing this might be patched-up in future - ?) Perhaps my biggest frustration with LBPK though - at present - is the small size of the online community, though hopefully this will change as Xmas nears and folks hear that the IGN 5/10 is actually a joke! Right now finding a full x8 'human' lobby is quite tricky...
Back on a positive side though, the kart handling is smoother than MNR, the motor / logic etc tools are more intuitive and easier to work with than LBP1/2, the AI is less annoyingly rubber-bandy than MNR, and the opportunity to have objects overlap each other or stay put without glue etc provides fresh ideas compared to both LBP1/2 or MNR.