My 2 cents: (Actually more like two dollars)
I have all the C3 sets, and many of the Marvel Minimates. I’ve also been a toy collector for a long time. I find that any toy that you assemble such as C3/ Legos etc is going to come apart easier than a toy that isn’t made to be assembled/disassembled.
Some of the C3 sets suck. The min-Batmobile set spring to mind (just for lack of features). Putting together the Batcave was frustrating. Others are better. The larger Batmobile is great. Nice details, however the one that I bought was missing a piece so I had to improvise. I love the batwing but with extended play some of the bottom pieces fall off. Again this set came missing a piece. No problems with either of the Justice League sets. And the Batcave aside from continually falling apart (see my Batcave post) is a nice set. So, it seems with the sets, the more pieces the greater the chance of it falling apart.
Sollution: super glue critical stress points. Should you have to superglue a modular toy just to keep it together? Well … I’m sure we’ll be debating that for a while but as I said gluing the pieces together is definitely a long-term solution, plus is seems like the future sets are all smaller, so hopefully this won’t be an issue.
As far as the figures go. I thinks it’s hit or miss. I’ve been lucky so far. I know some people who were getting their Marvel minimates with 2 right arms or masks that slip off. I think one again, that the modular nature of the figures are gonna make the toys prone to falling apart. The very thing that’s so cool about them is also the thing that many people complain about. If you really get irritated by hair not fitting right, super glue. I think the level of detail on the C3 minimates & all their accessories as opposed to that on their Marvel counterparts more than makes up for their other shortcomings. I also appreciate the round feet holes on the new minimates (makes them much easier to display).