Agathi Christie's Poirot

Are the books worth reading? I always see the TV adaptations on ITV but never bothered to watch one.

I'd recommend:

The Murder of Roger Ackroyd
The Pale Horse

First is one of the best of the Poirot series;  second not part of any series.  Also, if you like the style of British detective fiction of the "golden age", you really should read

E. C. Bentley, Trent's Last Case

This novel was written in reaction to the leading detective fiction of the 19th century (Doyle's Sherlock Holmes, Poe's C. Auguste Dupin), and in fact subverts the form - and yet became a key text for the "greats" of the earlier 20th century.  Also very much worth a read is

Wilkie Collins, The Moonstone