There is a world of difference between the two recordings, but it can be summarised very simply:
In 'Lute Songs', the words are pronounced in the manner of a 16th century Englishman, and despite my having difficulty understanding what is being said without the words in the sleeve notes, the emotional impact is presented with stunning clarity.
In 'Sweet stay awhile', the words are pronounced as in contemporary English, and I can tell every one without need for notes (which is a good thing as the words are not included!) but the emotional range of Charles' singing is far less apparent. The only point at which he approaches the quality of performance of 'Lute Songs' is during the final few religiously inspired songs.
What that tells me is that Charles used to be a fine tenor in 1998, but in the intervening nine years he has become something extraordinary. His choice of accompanying lutenists has also improved.