I didn't think this was possible. But i'll try to think of something...
Can't complain about one thing in regards to her music talent, but her PVs and album cover are B.O.R.I.N.G. They all look the same. They ARE the same. XD. E.g. All the CDs she's released have the same layout. Her on the front looking all pretty; Portrait layout; Few pictures; Her doing something with the piano on the back. Her album TODAY shows she is adding more pictures though...though with the piano XD
Has a frequent tendency to finish songs too quickly. All her lyrics get used up by the halfway mark, and then the rest is just music. A good example is Beautiful World or 虹色バス. There are exceptions of course like BLUE :D
Too much of a s***t. But is that a bad thing?!?!
Other than that, it would be that she needs to put more work into her compositions. She merely writes the lyrics.
Oh and write NO BORING songs. Dear Family was horrible.