Much of the 20th Century fits this bill
Bartok was the first composer that came to mind for me. The string quartets are astringent, bracing, and essential, in my opinion.
Oh, yeah, and dark too. Think of that Balkan temperament.
"Not really dark or brooding" in the friggin' extreme.
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I love Satie, but he's picnic music compared to Bartok, Stravinsky, Schoenberg, etc.
Damn, Try Bach, Beethoven, etc. Stick to the more austere forms -- solo instruments, string quartets -- and they should at least approximate your cup of tea. Just skip the romantics and you'll be pretty much assured of astringent angst, rectilinear rigor, and depressing dolor.