I've just read Nabokov's lecture on Dead Souls in Lectures on Russian Literature.
It will not be summarised, and should be read in full. However, there's 1 interesting point- for Nabokov, Dead Souls ends at volume 1, with Chichikov fleeing the town; volume 2 is a failure.
On my part, I don't think that the whole volume falls apart, but I do have some issues with the last chapter. Earlier I wrote, Gogol's not Tolstoy. And he's not. But there's 1 similarity- there are 2 Gogols as there are 2 Tolstoys, the artist and the preacher (Chekhov and Turgenev of course never preach; but such a dividing line, with constant conflicts between the 2 roles, I haven't seen in Dostoyevsky). In later years these 2 men were basically nuts. The difference is that Tolstoy, at his best, has balance and control, and, one can also say, sanity, and he's a realist- all the detailed descriptions add life and depth to the characters and the scenes and they all are connected so that his novels, loose as they appear, have a sense of wholeness. Gogol, in contrast, gets himself carried away by his imagination and streams of thought, crams a bunch of colourful characters into a rather thin book, fuses it with layers and layers of descriptions of irrelevant details and people who will never appear again... Dead Souls also has a sense of wholeness, but a different kind, everything fits together in their bizarre qualities and fits the overall pattern of the book. Gogol, at least according to what I perceive in Dead Souls, makes the best use of his own genius when setting himself free and getting carried away. Then he's being a pure artist. Once he wants art to have a purpose, once he turns into a moralist, a preacher, once he becomes conscious, rational and didactic, he somehow loses his touch. The persuasion, the intervention, the resolution, the speech, all of these feel slightly wrong. Note, in the previous post I wrote nothing about Kostanzoglo, Muzarov and the prince. It would be too harsh, and not entirely correct, to say that these 3 characters are there only to serve a moral purpose, but they lack something of the other characters, from Manilov, Sobakevich, Plyushkin, Korobochka and Nozdryov in volume 1 to Tentetnikov, Koshkarev, Khlobuev and Platonov in volume 2.
However, I should not exaggerate the failure of the last chapter in volume 2. The merits of the whole novel tremendously outweigh the faults, and this novel is a (flawed) masterpiece.