I suppose that
The Eternal Husband is obscure for a reason--specifically because it is such a minor work in the context of a writer as great as Dostoevsky. I didn't particularly like this short novel and overall I would tend to agree with Paola's assessment.
As Issybird said, two of the important characters are dead when the novel begins. As to the other two significant figures, I found that Velchaninov swung between extreme moods all the time and some of his actions really seemed to be entirely lacking in sufficient motivation. Trusotsky was memorable all right--memorably unpleasant and unsympathetic.
The book is still worth reading, though. There is the interesting--if limited--way that Dostoevsky reveals the inner workings of the mind of Velchaninov. Some of the minor characters stand out with some vividness--especially Nadia, the 16 year old being courted by Trusotsky. Her young boy friend makes an impression too in the one scene where he gets a chance to level with the older men.
The household of the lawyer with all the daughters is a great snapshot of the kind of activities by which they entertained themselves and their guests.
Poor little Liza dies so soon. I found her a very vivid character who created an impact in her brief life. Somehow, I feel that if she had lived the novel would have gained in emotional substance and Velchaninov's character could have been developed in a more balanced way. But that's only my emotional reaction to the character and clearly Dostoevsky wasn't interested in writing the longer and very different novel this approach would entail. But it is a tribute to the author's skill that in such a short space he was so skillfully and powerfully able to delineate the tragic circumstances of the child.
So----a minor work it may be and it does contain flaws, but even a flawed work by Dostoevsky is worth exploring.