Let's see if we can cut through the hype about Susan Boyle. I was a trained singer. I was a solo boy in a church choir and that takes talent as well as a lot of training. I was never great - I was just a bit better than the other boys whose voices had yet to break. A lot was expected of me and the voice training could be quite painful. I know what level I was supposed to aspire to, even though I might never make it.
Susan Boyle is not some undiscovered amateur who finally got her chance to use her talents in BGT. She has sung before and tried to get recognition. She has had exposure enough such that those who could spot talent could spot hers. She has made a few recordings as well as made a few appearances.
This is Susan Boyle at aged 22. She was singing in a club so it wouldn't sound great even if she did a perfect job. I thought she was very good in this performance. The musical accompaniment was dreadful and very distracting but she held the song together well despite this. Considering the conditions, I was very impressed with her performance.
http://www.etonline.com/news/2009/05/73488/
Here she is in 1995 presumably aged 34. She looks awful. She is belting out a song which requires a lot more sensitivity. She sounds awful. I have never liked Barrymore (he makes my flesh creep) and it makes her performance seem even worse but she obviously has no appreciation of the way this song needs to be sung and she obviously has not progressed as a singer since her club performance. She sounds worse.
In 1999 at aged 37 she gave a very good performance of "Cry me a River" for a charity CD. She seems more suited to this sort of number. She is using her natural voice and it fits the piece well. There is some lack of control in her voice but it is still a very creditable performance and a sign that she could build upon this with some proper training, find more suitable numbers to sing and be good enough to record a CD.
On the same CD in 1999 she sings "Killing Me Softly". It is a poor performance. The main problem is her lack of expression. Also evident is her lack of voice control. As the song progresses she lacks even more expression and sounds like she is just going through the motions of singing it.
So here she is on BGT aged 47. Nobody has heard of her. You would think she has never sung before in her life and she gives a feisty rendition that belies her age and appearance. She gets a standing ovation for what was an excellent performance of "I Dreamed a Dream". Most of the credit she got was from the surprise effect and partly from the guilt people had from writing her off by her age and appearance.
So she sings in the semi-final of BGT. It could have been the stress of her sudden-found fame and her exhaustion that resulted in a miserable performance. She lacks voice control, is warbly in inappropriate places and mainly she lacks expression. She sings "Memory" from Cats and is frankly awful. Her start to the song is even off-tune. She proves herself to be no Elaine Paige.
For the final of BGT she goes back to singing her debut song that she knows she can do well but it signals that her repertoire might be limited and that she might be a one-trick pony.
If you have listened to these performances then ask yourself if her voice is ready for the world stage or will ever be.