how refined are your ears?

IMHO, Andrea Bocelli and Sarah Brightman are in the same league. If they float your boat then by all means collect their CD's. I personally don't own any. I have been listening to the classical voice for over 25 years so by now have a pretty good knowledge and appreciation of a classical singer's art. A beautiful voice is definitely a good start, but it's the technique and art of delivering the line and the meaning of the text/lyrics that differentiate a singer's singer from a mere songster/songstress.
Callas does not have a beautiful voice but one only needs a few seconds of listening to her arias to recognize a legend.

And then there is Rita Streich. :>)

Why do questions like this get posted in the review forum?

If you want to know what great singing sounds like you need to listen to Jussi Bjorling, the GREAT Swedish tenor.
Period.

I'm going to submit for your consideration tenor Mark Padmore. He is well known for his his baroque works, but I also just love his recordings of the Schubert lieder with Paul Lewis. He has a unique way of saying more with less, if you catch my drift. To me, his Schubert has a rightness about it that can't be surpassed. They are lieder, not opera! See, now I've talked myself into cueing up Die Schone Mullerin.