@Arjen,
Part I, which is the major portion of the work was more or less completed by Wittgenstein himself, although the final form it might have taken if he had published it himself, is open to conjecture.
Most of the work consists of a related series of questions, observations and remarks, or as he calls them, "sketches of landscapes" (Preface) in a style that is philosophically unique to his new way of thinking. In defense of this conversational style, which arose "out of the very nature of his investigation", he writes:
"I should not like my writing to spare other people the trouble of thinking. But, if possible, to stimulate someone to thoughts of his own.
"I should have like to produce a good book. This has not come about, but the time is past in which I could improve it."
The book has been deservedly influential both as to its conclusions as well as its method of looking at problems.