I think Nick hits it on the head in reply to Ulvi:

>>Examples of what I have in mind of Mozart's ups and downs are the
>>last mvmnt of the G minor string quintet, where an absolutely gorgeous
>>introduction leads to utterly vacuous music ...  where a particularly
>>frivolous new theme tears into the otherwise tight fabric of the musical
>>argument, and other examples I can go dig up for you if you want.
>
>Mozart has no trouble maintaining serious, even grim, moods when he
>wants.  (Witness the C minor piano concerto and the G minor symphony.)
>...  It's not a breakdown of craftsmanship that we observe here; rather,
>there is a brightening of the concluding spirit that has come (since
>Romanticism?) to seem unsuitable.

I certainly don't like everything by Mozart, and I do consider some works
slighter than others.  Yet this shows to me Mozart's range.  The other
thing is that music since Beethoven has led us to expect a "profound" last
movement.  It seems to me that in the 18th century (Baroque and Classical),
the expectation of the last movement was to lighten and dispel.  There are,
of course, exceptions, Mozart himself providing a stunning one in the
finale to the Symphony No. 40.  Mozart's finale to the g-minor quintet is
light in this sense, with a charming (in many senses) melody.  For some
reason (and I detect a bit of it in Ulvi's parenthesis), people think that
melody is the cheap way out, whereas it's probably the hardest thing for
most composers to come up with.  As Vaughan Williams once remarked to a
Young Turk, "Very good, my boy.  If a tune should ever occur to you, don't
hesitate to write it down."

>Then, of course, there are Tovey's remarks about the conclusion of the G
>minor quintet: after the mournful introduction, the music says, "That is
>all, my children: the rest is too sad for you."

Great quote!

Steve Schwartz