Well, considering she is ageing she will probably never reach the same vocal prowess as Whitney, or Mariah or even Celine. She definitely can sing and she has a beautiful timbre, and a more than respectable range. My only problem with Bey is that she always seems to eager to show it and it is not always a complement to the song. It is not natural like Whitney's, she lacks Whitney's musicality. It feels forced and unnecessary most of the time. Of course she is no Christina on that regard, Christina is beyond hope when it comes to "oversinging", but Bey could tone it down sometimes. All in all, it is only personal preference here, so don't take my opinion too seriously.
Also: Destiny's Child Bey >>>>>> Solo Bey. Just saying.
Edit: I just wanted to open a parenthesis here to say that better than all of those is Christina Bianco, who is all of them (and more!) combined in one: http://www.youtube.com/watch?v=C3DlDPeurRw Please watch this if you haven't seen it yet!
Also: Destiny's Child Bey >>>>>> Solo Bey. Just saying.
Edit: I just wanted to open a parenthesis here to say that better than all of those is Christina Bianco, who is all of them (and more!) combined in one: http://www.youtube.com/watch?v=C3DlDPeurRw Please watch this if you haven't seen it yet!