you could basically say the same thing about a lot of films generally held in very high esteem here. Dreyer's "Day of Wrath" immediately comes to mind, Tarkovsky's "Sacrifice", lots of Bergman and Kurosawa ("Ran", "Kagemusha") as well. In all these films, it's precisely the 'doom' that makes the story engaging for me, the humanity displayed or even only brought out in the characters because they are fighting that inescapable fate.
Day of Wrath, Ran, and many other soul-crushing films number among my favourites - indeed, I too tend to think of the 'doom-laden' aspect of these films as being the thing I love most about them. Which is why I was so puzzled by the boredom I felt while watching Chikamatsu. I only started to enjoy it during the Lake Biwa scene, and was fairly engaged for the rest of the film - the scene where Mohei and Osan are torn from each other was as good as the equivalent scene near the beginning of Sansho, and there is definitely something uplifting, as well as tragic, about the ending...
Curiously, one of the online reviews of the disc called "Chikamatsu" a 'soap opera', and indeed I find this film in a certain way more 'sentimental' than the other films you mention. Though again I'm not sure that sentimental is the right word.
I suppose what I meant by saying Chikamatsu isn't 'sentimental' enough is that it doesn't establish the relationship between Mohei and Osan in sufficient depth or detail to make me really care about them. I only cared insofar as the sensitive performances made me care - come to think of it, Wyler's 'Carrie' suffers from the same problem, that is, that the 'illicit' relationship isn't fleshed out enough. The characters seem to operate more as symbols, or chess pieces, than as real human beings. Whereas, for instance, Celia Johnson and Trevor Howard in Brief Encounter not only give great performances, but are also working from a script which gives them the space in which to develop a rapport. I get the feeling this is something that some directors can do and others can't - and I have yet to see a Mizoguchi film with a convincing romantic relationship in it. (And no I don't think the one in Musashino counts, though I love the film.)
Day of Wrath doesn't depend on our caring all that much whether Anne and Martin make their relationship work, and indeed the moment when Martin betrays her at the end comes as no great surprise - it's a very satisfying resolution of the tragedy. Their relationship was about as well described as that of Mohei and Osan, but the romantic ending to Mizoguchi's film has not been built up to enough to make it a truly satisfying payoff.
As for Ran, that to me is a film that, like Die Nibelungen, works on the epic scale, not the personal, and I feel almost nothing for any of the characters - Chikamatsu is not an epic, but a melodrama which succeeds or fails according to whether you feel for the characters, and for some reason I didn't.
Plus I was in a bad mood when I watched it. I'll probably like it better next time.