The problem with MM is that it is not currently designed as a very rewarding class to play. There is no moment of glory to base your rotation around, things like Fury rampage and the spec being built around getting as many of those as possible, or Fire mages being built around stacking crits for Pyroblast.
While Aimed Shot is not constantly spammable, it does lack any mechanic around it that really emphasizes its role on the rotation. Compare this for instance with Destro lock, where you could simply spam Chaos Bolts, the way the spec is built emphasizes that a well placed Chaos Bolt is a reward for playing well.
Some have argued that the core of MM is Focus management, but if it is then that might be even worse, MM really only has two abilities that regen focus, and one of them is dependent on external power to be worth using.
MM is a class of good ideas stacked on top of eachother without a seeming idea of how they are even supposed to fit together.
And there is of course also the fact that most of the talent tree is awful, and again doesnt really seem interested in emphasizing any part of the core rotation other than adding more unconnected abilities to it or slightly buffing others.