Poirot is a very good show and if I have never read Agatha Christie`s novels about this character (and I`ve read almost all of them), I would have evaluated it much higher (but now my grade is only 7).
Every aspect of the show is great except one - lots of episodes differ from the original contents of the novels they are based on and sometimes it irritates me. But nevertheless it is always fun to watch every episode only because of the great perfomance of David Suchet.
Also, this show is a part of my childhood. I remeber watching new episode every friday on ORT (russian TV channel) with my mother. And now that I have a DVD collection in my possession, it gives me a warm feeling every time I see an episode I remeber watching 10 years ago... So, it has a sentimental value for me too. I liked it more back then though, as at the time I haven`t read any of Poirot stories.
So, the point of my review is (an this is only an opinion) - if you have never read about Poirot, you will be in love with this show (if you like the genre) and if you HAVE read the books, you will like the TV show anyway, maybe just a little less.