I have to admit the sheer complexity of the paid version is what's keeping me away from paying anything near full price. The demo was fairly simple - attach a stupid amount of boosters to a nose cone and hope for the best, but recently i've been watching lets plays and it seems to be far more complicated to do similar things and i'm just not sure i'll be on the right side of fun vs frustration.
I suppose it depends on how you play.
If you start out in career mode(restricted funds and parts) with hard settings(no revert to launch/hangar for when things go wrong) and just start experimenting, you may well get frustrated if you ignore the contracts(income source) and keep running out of funds.
On the other hand, if you start out with the sandbox mode(no limits on funds or parts) and get the feel of what works and what does not, you should enjoy the game much more.
Alternately you could start in science mode(unlimited funds, but you need to collect science to unlock advanced parts), to first learn the basics then add complexity as you add in new parts.
Also, there are quite a few players who have various tutorials and such on youtube and there should shortly be new ones for the new version. (search youtube for Scott Manley if you want to see plenty of tutorials from a seriously capable player)
If you enjoy fireworks, you may just find yourself making deliberately bad design decisions to see how spectacularly they blow up... (recommend you use sandbox mode for this)
Finally, if there is anything you do not care for or would like to change in the game, 'there's a mod for that.' Personally I like Kerbal Engineer Redux(gives you calculated thrust-to-weight and delta-v per stage both while building and while flying as well as many additional useful details like altitude above terrain and how much higher or lower you would need to be to do a vertical 'suicide burn' to get to 0 altitude and 0 vertical velocity at the same time), and Stage Recovery(in career mode it gives you a partial refund for parts that would survive landing when they leave the physics bubble)