The Mysterious Affair at Styles is both the first Poirot novel and the first book Agatha Christie had published. It's an impressive debut, with turns in the story I did not see coming, and Poirot is an instantly compelling detective. 

As much as I genuinely enjoyed the book, I didn't feel that it's one of Christ's best. The final reveal was clever and made sense but I didn't personally find it satisfying. I also found the character Hastings really quite annoying, which hasn't been true in later books I have read featuring him. 

Overall I enjoyed this and would recommend it, especially to anyone who wants to know how it all began.