The problem is most of the fun comes simply from taking it all in. Throughout the main story mode, presentation is clearly put above challenging and satisfying level design. There are many obstacles and enemies you meet that force you to come up w/ creative solutions to get past them--often times incorporating the Vita's touch controls--but rarely are these combined in such a way to provide a true challenge. There are a few rare difficulty spikes but these are typically a bit more annoying than they are challenging. Plainly put: Little Big Planet is a platformer where the platforming is not all that good.
This being said, LBP Vita's saving grace is that though the main storyline revolves heavily around mild puzzle solving and platforming, that is not all it does. There are tons of mini-games--many of which would easily be worth a couple of bucks as PlayStation Minis--and some of them are more fun than the platforming sections. These games also serve as an introduction to what the very powerful (and extremely complicated) level design tools incorporated w/ LBP Vita are capable. You can not just make additional LBP levels but whole new games that really don't look or feel anything like the game you were supposedly buying. The community generated content has really begun to grow at this point and though it can take some time to find them, there are already some excellent games and levels to be had.
For this reason, I can heartily recommend LBP Vita despite the fact that the main story is not up to the same level of platforming as, say, New Super Mario Brothers or Rayman Origins. If you are looking for just a quick playthough of the game, you may be disappointed but those willing to delve through community generated content--and especially those community members who like to generate the content--will surely find quite a bit to enjoy here.