Before I write down what I thought of this work, I'd direct anyone trying to seriously grapple with early Lukács to David H. Miles' 1979 essay "A Portrait of the Marxist as a Young Hegelian: Lukács' Theory of the Novel," (PMLA vol. 94 no. 1), which is a really clear exposition of the place of this book in Lukács work and its relation to German idealism before it and to Marxist literary criticism after it. Also only 14 pages long.
The Theory of the Novel has a fairly unusual and difficult writing style. It almost exclusively uses abstract language - there are only two or three paragraphs that meaningfully discuss actual plot details, in the concluding chapters on Goethe and Tolstoy - and it never varies this diction, moving pretty swiftly through its theoretical opening to its typological survey. This abstract language is mostly Hegelian (or at least "pre-Hegelian," to use Paul de Man's term), but it is not inaccessible and if anything it can be a good introduction to this type of writing - German idealism in general - since there are many much longer and denser works in the tradition. It's also full of poetic moments, particularly in the first half: the opening chapters read almost like a prose-poem commentary on Ancient Greek culture and philosophy, and it can be quite beautiful.
In trying to get my head around this work I feel compelled to comment on these unusual stylistic properties. It becomes I think weaker towards the end, as we proceed through an in-no-way-exhaustive survey of great novels, none of which actually represent unmitigated successes for Lukács - they all fail in one way or another to return to the epic (except Dostoevsky, who requires another book, never to be written!) and as Miles explains this kind of points to the central weakness of this (and many other) German idealist accounts of art, viz. the ideal, both of form and content, lies in an imagined golden or classical past (which was actually a stratified slaveholding society). It seems somewhat weak, somewhat unsatisfying, to read a series of quick accounts of Cervantes, Goethe, Flaubert, and Tolstoy that focus on their failures at the expense of their concrete successes or immanent details. Lukács also has quite a sweeping and generalising feeling for the historico-philosophical moments (to use his hyphenation) of each of these works, which makes the accounts seem distant and unenlightening. His prose is powerful, and almost otherworldly, at the beginning of the work, as though Lukács were actually performing (as he very clearly does in the surprising first sentence, which just throws you into the past) his thesis that there is a 'philosophy of the history of forms' and that forms can speak this philosophy into being. This prose is happy to trade in abstract concepts because it is classically and confidently philosophical: it has things to tell you about essences, about soul, object, and world.
Here is a useful long quote: "the Greeks traveled in history itself through all the stages that correspond a priori to the great forms; their history of art is a metaphysico-genetic [not totally sure what this is] aesthetic, their cultural development a philosophy of history. Within this process, substance was reduced from Homer's absolute immanence of life to Plato's likewise absolute yet tangible and graspable transcendence; and the stages of the process, which are clearly and sharply distinct from one another (no gradual transitions here!) and in which the meaning of the process is laid down as though in eternal hieroglyphics - these stages are the great and timeless paradigmatic forms of world literature: epic, tragedy, philosophy. The world of the epic answers the question: how can life become essential?" (35). I think when first reading this passage it didn't hit me that Lukács had slipped philosophy in with the two other genres and explictly labelled it a 'literature.' He doesn't really need to answer a lot of the questions that we might conventionally pose the literary theorist, such as 'why read literature' or 'what does literature tell us about the world or our society' because here it is basically evident that all these textual productions share the aims of philosophy: it's about the examined life, examining your concepts and getting to essences and truths.
Lukács develops this thesis by talking about the role of the subject as artist. The writer has an "ethic" (pp. 66, 115) whereby they articulate their (soul's) relationship to the world and to essences, and in so doing we learn about how social structures (at least insofar as they are represented in novels) either do or do not facilitate the soul's grasping of itself and of objects and essences.
Lukács doesn't really consider the act of reading in this book: he uses subject interchangeably with writer, as a translator's note points out, and the thing that he's analysing is almost less the content of the novels than the method by which the artist-subject assembled them (or formed their totalities, which no longer simply copy the world but must recreate its lost unity) such that he can tell us in concrete detail about how the soul of the writer grasps an essence, i.e. Socratically or otherwise. We might worry that there's a bit of a gap here concerning the reading rather than the writing subject, but I think Lukács' conception of novels does not totally contradict Barthes'. The Lukácsian novel's philosophical work, its philosophical richness, is maybe not dissimilar from Barthes' writable text: like a Platonic dialogue, it takes you, and your soul, through a journey or a process, perhaps dialectical, towards the understanding of an essence. It's not that Lukács unduly elevates the author-function or the transcendental signifier: on the contrary and ironically, all of Lukács' authors end up quite similar to each other, because they are all, for him, engaged in exactly the same task, and fail according to the same criteria.
This was a good and difficult read. I recommend having an interest in at least one of the authors whom he discusses, or in Ancient Greek literature (or perhaps Virgil, who is criminally underexplored by Lukács!), because there is much to critique and expand on here. I also sincerely recommend reading the 1962 preface after you have read the actual text, because it doesn't really elaborate or introduce the material, but is instead partly an interesting contextual note and partly an auto-critique. It helps I think to pull you out of the strong stylistic voice I have identified and into an awareness of the incompleteness of this work as a youthful moment in Lukács' overall development (interrupted by his own historico-philosophical circumstances, as always).