I understand what you're saying, but I just don't experience Brahms's music like that at all. (It's strange, I've never had this Brahms problem that almost everyone else seems to have had to overcome at some point ...) To me it's subtle music, both technically and emotionally; deep rather than obvious, and leaving plenty of room for the listener's imagination. How curious; maybe we just know different pieces or something.

My feelings are closer to those of ollie and t-i-n, but they haven't always been like that. When I've been at my most ungenerous to Brahms (who I really did not like through my 20s) it was less to do with the music being over-explicit (I really don't feel that at all, and never have done - I've heard the Second Symphony many many times, and still it remains mysterious to me in many ways - and that's true of much other Brahms, it rarely seems totally 'graspable' (which I intend as a compliment)) rather that it can seem somewhat 'over-composed' at times. The First Symphony and particularly First String Quartet do suffer a bit from this quality to my ears - he can't let a few notes go by without subjecting them to intense development, sometimes worked fully through by the time one has reached a point 8 bars later or something! But not everything or even most of the work is like that, by any means. Listen for example to the expansive melody in the First String Quintet, or some of the mid-period songs. And elsewhere, at his very best, he manages to marry a certain vocal lyricism or allusion to folk material with the very highest degree of developmental and contrapuntal skill - I would go so far as to compare this innovation (which to my ears far surpassed the interesting but ultimately rather surface-focused types of 'Hungarian gypsy' exoticism in much of Liszt) with the marrying of Italianate melodic traditions with Franco-Flemish polyphony that occurred in German music in the 18th century.

In terms of maligned genres (as was suggested of opera), I'd offer up choral music in general as one such candidate! So much wonderful stuff from many composers (I'm not just thinking of German ones - take the amazing stuff of Janáček, say) but which is usually assigned a relatively marginal position within composers' output.

Yes, I identify very closely with this feeling about Brahms...  he's not a "readerly" composer, and I feel that he's thrown down the glove and said "like it or lump it, Joh. Brahms, so there".   It's this arrogance in his music - and in much other German music - that leaves me feeling that it's not written for listeners..  it's written so Brahms could get it out of his system.  I feel I've been bludgeoned whenever I listen to him.  I'm sure it's all been very worthy, but it hasn't involved me at all.

Brahms's music certainly exhibits has an inward and even private quality (as apparently, also did his playing, which was criticised on these grounds in opposition to the more flamboyant virtuosi of his time - Brahms seemed to have little interest in 'playing out' to his audience). But that to me produces the very opposite result of that described above, it makes it more rather than less 'readerly', less imposing certainly than the more extroverted rhetoric of many of his contemporaries. In terms of such an approach being 'arrogant', that sort of criticism has been made of various composers over a long period of time (not least of Beethoven, right up until the present day), and ties in very closely with the Taruskin-type polemics against a post-Beethovenian aesthetic whereby music went wrong when it began to be written according to the desires of the producers rather than consumers (there's some very interesting stuff in John Butt's Playing with History having a go at these sorts of arguments of Taruskin, in their earlier guise in Text and Act). Personally, I doubt very much lasting music has been written primarily by trying to second-guess listeners' desires, and the best pre-Beethovenian music was produced in such a way despite the structures under which the composers worked, rather than because of them (and the same goes of composers today trying to satisfy other institutions and the marketplace).

Indeed. I can relate what strina says, about music that 'struggles and strives for something it never quite reaches, or even deliberately turns away from just as it's getting there', to my experience of Brahms much more readily (although I don't personally find it a big problem), but that's surely the opposite of saying that the music is 'too explicit, leaving nothing to the listener's imagination, he seems unaware of the possibility of implying something ... rather than stating it in forthright terms and then underlining it for good measure'.

Which brings us round to where the thread started...  does Brahms ever allude, or does he just "state it in forthright terms and then underline it for good measure"?

Perhaps there is some underlying conclusion about the role of an artist to society...  that a German artist feels no responsibility to his audience, who must instead strive to accept and understand his art-work...   whereas there is a more interactive relationship in other countries?

I listen to Brahms with a sense of duty - I see how carefully written his music is, how taut his first-movement logic is,  all is high-quality and very competently done.   But there's no marvel in it. 

You mean, like some of us are doing on this thread with our Brahms aversions?