Interesting question and some equally interesting nominations. However, I
don't think we have dug deeply enough. First, let's define
"underrated". Do we mean underrated as concerns familiarity
(based on frequency of performance) to the listening public of even above-
average sophistication; or do we mean critical recognition within
musicological circles? They can be two very different things. IOW, a
distinction needs to be made between underrated and neglected. For
instance, Alban Berg is, without a doubt, one of the very greatest twentieth
century composers, but one who the vast majority of "classical music
lovers" are not familiar with. From that standpoint he is vastly
underrated; but, within musicological circles he is most certainly given his
due. At the opposite end of the "accessibility" spectrum we
have George Gershwin. Here is a composer who, while vastly popular, is
unfortunately relegated to the status of "classical-lite"; even
within some critical circles. Some of his works like "Concerto In
F" and even "An American In Paris", while eminently
accessible to the listener, are compositionally brilliant and deserving of
recognition alongside more "serious" works. In spite of his
inaccessibility even Berg is programmed on a somewhat regular basis (the
Met has programmed "Wozzeck" for this season).
The same goes for most of the other nominees, which disqualifies them
from "most underrated" status. I agree with Brownsfan that
Britten deserves much more frequent performance, but hardly a season
goes by at the Met Opera that doesn't include a Britten opera (A
Midsummers Night Dream this season and Billy Budd last). Bartok is
definitely not a contender; his concerto for orchestra is a staple of the
orchestral repertoire. John Adams has unfortunately been lumped in with
the other "minimalists". He is a truly brilliant composer, but
hardly unknown or underperformed. Phillip Glass? Well, he can't even
shine Adams' shoes, shoes, shoes, shoEs, shoEs, shoEs, shOes, shOes,
shOes :-) Janacek is a good runner-up, but I might be inclined to instead
nominate Zoltan Kodaly, Francis Poulenc, or perhaps Alexander Glazunov,
who like Janacek just squeezed by for qualification as twentieth century
composers having composed from the late nineteenth into the twentieth
centuries. The Glazunov violin concerto is one of my very favorite works.
I think that Martinu is a good call on several counts; a brilliant composer
who is particularly deserving of wider recognition especially in light of the
fact that he was extremely prolific. But, even his works are popular in
conservatories and the more adventurous programing. So, my nomination
for top spot has to be the Swiss composer Frank Martin; extremely
interesting music influenced by twelve tone row techniques without
abandoning tonality, and a name that most are not familiar with. For
anyone interested his "Petite Symphonie Concertante" is a
great place to start to learn about his music. Still a young man, but began
his composing career in the twentieth century and sure to be nominated for
most underrated 21st century composer is Thomas Ades.