James Nicoll reminds us of Brian M. Stableford's Hooded Swan series, which I adored back in the late 1970/early 1980s:
The Hooded Swan stories are gloomy and morose to the point of parody. If it were possible for space to be overcast and drizzling, it would be so everywhere Grainger goes.
I have to confess that I barely even noticed this. Then again, it was the 1970s and I was British.
[Stableford's…] later work is more ambitious, but not always as enjoyable as these stories. Though perhaps "enjoyable" is not the right word. They’re readable. Perhaps they would have been more enjoyable if the protagonist hadn’t been an antisocial depressive.
If you are looking for morose space opera told from the point of view of a misanthrope, featuring puzzles with depressing answers, you might like this series.
I feel like being a fan of this series set me up to fully enjoy Ian M Banks' Culture novels. The Banks novels were set in a very different universe and starred a very much more capable set of protagonists who would have looked on in amusement at the crudity of the technology that Grainger and co were blundering around using in their attempt to understand their little corner of the universe[note]Let's face it, an agent from Special Circumstances would have got to the bottom of the mysteries encountered by the crew of the Hooded Swan in five minutes flat with a little help from access to the data the Culture had to hand.[/note] but it feels as if slumming it in the technological dark ages with Stableford's crew was necessary for me to fully enjoy the very different view of the universe granted to the agents of the Culture.