TLW isn't quite in the same league as the first book in my opinion, but the review Aspie pulled up is a steaming pile of fresh rhino manure.
There's a lot of thought-provoking theory in the book, and looking further into it can be a journey down the rabbit hole. Once you start looking at problems in evolution, you start looking at self-organising behaviour, which in turn leads to Fibonacci sequences and some incredibly bizarrely ordered patterns that occur in nature. It's a book about theory more than anything else really, in my opinion, and exploring further depth in concepts addressed by the first book. The other major element is exploration in the modern age, which Crichton handled more thoroughly in Congo.
As for the film, I'm not too bothered that it deviated so far from the book, but I think they missed an opportunity to give it a proper message that you'd walk away with as strongly as the potentially deadly consequences of cutting-edge science in the first film. TLW brushed up against issues of conservationism, and the merits of preservation versus exploitation, but it didn't press the matter home.
And that's an opportunity that's probably lost for good now, there was never any chance that JP3 would have 'something to say'.
:edit: added part 2 and applied topical cream on some midnight posting syndrome.
