I initially decided to stick with 3 stars, as I don't shell out marks so easily! Lol! But that fact which makes this book one among the 1001 is that it was published first in 1926, and still holds such an interesting ground for mystery novels. So I loosen my grip on 4 here.
Considering almost 8 decades since it was first out, I give full marks to the mystery part, concealed facts, and never disclosing them till the end. Introduction of Hercule Poirot is definitely un-expected. Narration of the story as statements, and supportive facts can help a normal man to think like Hercule Poirot. The candid, and continuous conversations between two conversationalist (instead of naming the speaker) makes it a unique style of Agatha to flourish the interest for the story.
Further, whenever I read a mystery, my effort always is to walk hand-in-hand with the detective. Here too, I made my mind knock at every door and bring everyone in the circle of defect, except the real suspect!
The richness of Roger Ackroyd attracted him friends and foes. He had a few family members and an equal amount of servants and home-makers around him. Thus murder of Roger Ackroyd was a profitable business for more than one member in the family. However, more than the family, the housemaids also have their shares of concealments, and gains from his death. The task for the famous H Poirot is to uncover the false and unveil the dubious body.