See, I was never a fan of her voice. Actually, initially I never liked her just because of her voice. Even today, when I sit in the theater I kind of feel irritated in the beginning 5-6 mins. But, as and when the movie gets passed by this time , I am glued to the screen, I can see her sole domination over the movie.
She completely justifies her role and takes up the script by herself, always, yes always.
I became a fan of hers when I watched the movie- Fashion , her confidence as a supermodel, her attitude towards acting truely demonstrated her dedication to her work. She actually sidelined a well established actress 'Priyanka Chopra'. She even received National Film Award for the role of best supporting actress and also the Filmfare for the movie.
Have a look!

And it was aptly judged by the directors when they started making Kangana centric movies.
The best actor award for Queen , no one can take away the master performance of Kangna Ranaut as Rani. This is by far her best performance. Her deglam look in the movie is undoubtedly, one of the best.

And then came Tanu Weds Manu Returns, where she acted with both glamourous as well as deglam look. The bullet hit the bull's eye again. If she was overrated, she would've gotten the biggest opening on the very first day. But, no! The movie revenue grew and scaled up dramatically as days passed.

Her stupendous acting skills have overshadowed her voice.
She is a genuine personality. Even after being one of the biggest actress in the industry, she has admitted that her English is poor, and yes she admits that she need to work on it.
She takes adequate judgement, is selective in taking up movies. She nails it most of the time.
She has a clear view of herself and about whatever she has actually achieved.
Just take a look at Shoor Veer Singh's answer to What is the wisest thing said by a Bollywood/Hollywood actor/actress during an interview?
and
Take a look at this Himanshu Kumar's answer to What are some of the best examples of "beauty with brains"? too!
She doesn't seem to be overrated. She doesn't boast. She is Kangana! Stylish, confident, glamorous and a perfect decision maker, be it w.r.t. Movies or Brands. ;)