I was going to buy some Kre-o to test the quality of them. How are they?
I dont have any of the big sets (and dont plan on it), but I have some of those blind-bagged minifigs and these two bad dudes

In my opinion the kreons are infinitely more fun and posable than lego minifigures, their arms and legs are on ball joints instead of swivels, and you can clip c-joints onto their arms or insert poles into their legs so you can do all sorts of things with them. However I have noticed stress marks around their hands and one of mine has a sort of loose arm. But to me those aren't deal-breakers. Building the combiners requires you to pull the arms off of one member of the team and they've been holding up pretty well anyway, so it seems the plastic quality is acceptable.