The murder of Roger Ackroyd is undoubtly one of the most famous works of Agatha Christie, with many stating that it is her masterpiece. However, I personally only liked it as much as many of her other works, perhaps because I accidentally read a spoiler of it while reading the review of another book.(spoiler ahead)
Knowing the identity of the murderer beforehand definitely made my reading experience a lot different, as the book was essentially known for its clever and novel plot twist of the narrator being the murderer. So in a sense I did not get to experience the exhilaration that one should normally get from reading the last one or two chapters of the book.
Instead, I was reading this book like I was reading it the second time, trying to pick out clues that were distributed throughout the novel. For instance, I realized the true reason of why James Sheppard did not want to get Poirot involved in the case, and why he seemd to have included any of his internal thoughts in the narration— any normal person would have wanted to take a guess at who may or may not be the murderer. This made the reading experience fun in a different way.
Still, I think I would have enjoyed the book more if I didn't know about the ending beforehand. The satisfaction of picking up clues early simply isn't comparable to the excitement of guessing the murderer and the exaltation of learning the plot twist!