I picked this up because I recently spent a weekend in Baden-Baden, the German spa town which provided (some of) the inspiration for 'Roulettenburg' in this short novel.
The central theme is the contrast between life when gambling on the one hand and everything else. Through its intensity, gambling makes all other aspects of the characters' lives seem trite and monotonous. This creates a sense of existential despair which feels very modern.
The gambling scenes are not enjoyable to read - there is a mania which grips the players which is deeply disconcerting. The pleasures of occasional victory are incredibly transient and limited to within the gaming room. On the occasion that the main character Alexei Ivanovich does manage to leave the casino with a fortune, he does not enjoy spending it. The scenes in Paris when he is extravagantly blowing his winnings with his spendthrift mistress Madam de Cominges are peculiarly joyless and really just an intermission before he can start gambling again. In fact, the more one thinks about the book, the more one realizes is that the draw of gambling is not the winning but the losing, of going to zero. I can't work out whether there is a valid sexual metaphor here or not – it's the sort of image I would have had no compunction about using 20 years ago, but I am now a little more circumspect.
There is a huge amount in this short book and I really enjoyed it.
One other point: one of the recurrent images in the book is of hordes of Russians swooping into this small German spa town; my experience in 2014 was not entirely dissimilar as there seemed to be big groups of Russians all over town. However, I understand that they gamble less now and are now more interested in getting their money out of Russia and investing in hard German assets.