There were always a few things holding back LittleBigPlanet from true greatness, at least as a top tier platformer:
- floaty imprecise physics
- separate foreground layers that you had to awkwardly switch between, both manually and automatically
- can't control sackboy with d-pad
- the square button being used just to access your menu, instead of main character actions like power-ups
- limited default moveset
I just think those early design decisions crippled the main series' potential from the get go.