I read the book before seeing the film, and as such the film didn't impress me much on first viewing, (though it has grown on me since), and I think that's largely because the book's greatness is down to its detailed understanding of Ripley's character. The film was a big glossy Hollywood number which went instead more for being a straightforward thriller, and you shouldn't really despise it for that reason, as it's a good movie. To make a film that stuck more religiously to the book though you would have to make it a much more offbeat, perhaps low-budget, affair.
The characterisation of Tom Ripley in this book is faultless. You do get much more idea of him as a person, particularly in the short but effective flashbacks to his troubled childhood (which is also where you gain your sympathy for him). His journey to Europe and the tangled web that is weaved there is extremely absorbing. In the Venice scenes too you get disturbing glimpses of Ripley's horror of close physical contact with the female sex, even to the extent where he is revolted by seeing a lady guest's underwear draped over her bedroom chair. It is hardly surprising that Patricia Highsmith has drawn such a complex character study, she was infatuated with her creation, to the point that she would sign letters from both herself and Tom!
The other books in the Ripley series are well worth reading but, to my mind, don't quite match the first. A lot of Ripley's mystique disappears when he's leading his comfortable artsy-fartsy life in France, (and in "The Boy Who Followed Ripley", a very late book in the series, I felt Highsmith was a tad TOO delicate about his sexuality, although the Berlin scenes have a sort of 1970s fascination), but in this, the first, where he's a loner travelling across Europe, this is a must-read.