From today's perspective, this novel is nothing more than a document - a document of the time when it was written and a document of how novels were written in that time.
From what I understood - being not a ottomanist myself - this is one of the first modern Turkish novels in the Western style. It was written in 1870s and it deals with two major issues - one is the question how to live one's life to be happy, the other is the blending and/or cultural fighting between the East (classical Ottoman) and the West (19th century Europe).
The author exemplifies his ideas using two characters - Mr. Felatun, who is a fool and very rich and in the end loses his wealth but gains some sense as the narrator understands it; the other is Mr. Rakim, who is of rather poor origin, but is extremely diligent and capable and ends up relatively rich and, above all, happy.
Another important part of the book, the narrator of this book leads constant dialogue with the reader, using sentences like "Do you think that Mr. Rakim should do this rather than that? Don't be foolish, dear reader" and gives his opinions and provides moral compass.
I am going to evaluate this book from the perspective of a modern reader, not a specialist on Late Ottoman literature.
What is good about this book?
It shows us the world, which is now long gone - the late Ottoman era with household slaves who were treated better their contemporaries serving in Western households.
Also, it sheds light on an important aspect - misconceptions of the East about the West - e.g. Josephine, a Western lady, offers to stay the night in the slave girl's bed... I very much doubt that any Western lady of late 19 century would willingly share bed...
Or the fact that English girls, who for some unexplained reason ended up growing up in Istanbul, would be almost automatically assumed to marry their cousins (from Alexandria or Izmir, at that!). It seems that in this, Ottoman traditions were projected to the Western world.
What is bad about this book?
Pretty much all the plot. There isn't an ounce of plotting, planning in this book. The books opens with a tedious description of appearance and character of Mr. Falatun and his sister. Later, however, the author loses all his interest in this character and he emerges now and then and a side character, with even the narrator acknowledging that this book shouldn't be about Mr. Felatun in the first place. Felatun's sister has an even worse fate. She is first thoroughly characterized, then left in the last third with a paragraph summarizing what happened after she got married (off stage).
Moreover, there are many pages which should have been omitted by the author. For example, there is a poem recited, without obvious relation to the narration, then it is interpreted (for half a page). Why? Or: an explanation on Turkish alphabet is given... one can hardly imagine, how someone reading the novel even in the 19 century would need or find this explanation useful. Of course, it is a plot device to ridicule poor Felatun, but it could have been handled much smoother.
Moreover, none of the characters is quite believable, least of them Mr. Rakim. Some part of the plot borders on the fantastical - for example, love, or even better: reciting Persian poetry, leading to tuberculosis.
Mr. Rakim's part of the plot is exceedingly boring, as there is very little conflict going on. Everybody knows that Mr. Rakim is perfect at everything, and if poor reader happens to forget that, the ingratiating narrator is only happy to remind him.
I wonder if the book would have been popular it translated to European languages in the 19 century. However, the most likely answer is that nobody would read it or care about it.