Very unpredictable

To my mind, Agatha Christie is one of the most inventive and less predictable authors. As for “ The mysterious affair at Styles”, during all the reading I tried to guess who the murderer was (or the murderers). I suspected at first one character then another etc. The author had given many hints to reader, some of them I have understood, the others I have misinterpreted.
One more thing I like: At first the behaviour of some characters seems absurd, but then occurs that every character has solid reasons to behave like that.
It seems to me that the narrator, Hastings is alike Watson in Conan Doyle’s stories. Because both (Watson and Hastings) admire the talent of detective. And both are in the same situation: their friends-detectives didn’t tell them the details of crimes until the end.
I like the image of Poirot, his attention and tolerance, wide knowledge, his love of order and neatness in everything. But I didn’t think that a detective can be so emotional.

Is it obvious after reading her books that Poirot had caught the correct suspect, that it had to be that suspect and could be no one else?