As I recall...
-The FAMAS delaying system was apparently tuned to a different 223 loading, so they cannot safely/reliably use normal NATO stuff
-Takedown of the bolt was fairly weird; something to do with a little part called the "Mickey Mouse Head" getting misplaced
-The furniture (I forget if it was the operating parts, too) was pretty delicate, and parts would start falling off, so there is a lot of duct tape
-At present, the vast majority of the guns are very clapped out*, and I believe not even France has a source for replacement components at this time (hence the carbine trials over there, even though there is little money or appetite for military spending, at least until quite recently)
-Other than I think an aesthetic/rail update (mostly done to replace aforementioned crappy furniture) I don't believe there has been much evolution of the delayed-blowback FAMAS design, which makes it less compelling than highly-developed AR15, AK47, or AR18 offerings.
TCB
*This is the saddest part, since even if France's hoplophobes weren't going to shred the guns, which they are, they'd be pretty much useless for us homebuilders. As bad as the G3's get, you can jimmy-jack your way back into a usable gun with oversize rollers and locking piece shaping --the lever-delay of the FAMAS is simply much more complex to tweak and manufacture