It looks a lot like a coup, except it isn't (yet)... no clear word on where the Presidential party is, but the troops haven't taken them although some ministers of the government have been. It certainly is an absolutely crippling revolt by elements of the Mali Army.
The reasons (officially) include the usual laundry list of claims against the regime, but one stands out: The Army has been engaged in a nasty fight against Tuareg insurgents who have lots and lots of arms left over from their days helping out on the side of bad in the North African crises, specifically Libya. The Mali Army forces were sent north to take them on with less-than-complete kit ...not that the regular Mali Army arsenal is anything to brag about... and have gotten handed defeat after defeat. Morale in the ranks of what has been a modestly respectable standing army collapsed and their blame focused on the Defense Ministry.
This matters, besides the usual reasons of not wanting rebellious troops rampaging through one's city, because the nexus between West and North Africa has been one of the few areas of growing strength for al-Qaeda-linked Islamist militancy (building on, if not supplanting, the usual bandit culture of the back country areas).
Losing the assistance of Mali in that fight, even for a short while, is bad for all of us.