For the purposes of this question the 1960 film version will be referred to rather than the 2002 film version, which takes many more liberties with the original text. The principal difference between the book and the film is the way that the Eloi are presented as humans and also the ending of the film hints at a happy ending between the time traveller and Weena, whom he goes forward in time to meet again. These are important differences, because they detract from the strength of the message of the original text, which concerns the need for suffering and change in order for humans to continue to strengthen and evolve as a species. Note the following quote from the text:
We should strive to welcome change and challenges, because they are what help us grow. With out them we grow weak like the Eloi in comfort and security. We need to constantly be challenging ourselves in order to strengthen our character and increase our intelligence.
The Eloi in the book, and to a lesser extent in the film, are presented as weak, helpless and vulnerable, because they have lived life in too much comfort, and therefore have not been forced to develop and adapt because of hardships. The presentation of the Eloi as being human in form, whereas in the book they have clearly evolved physically from our human state, does not help to reinforce this message. In the same way, the hint of a happy ending detracts from the rather grim message of the text, that seems to leave little hope for the future of humanity, with only the two flowers left to Hillyer symbolising a vague form of hope in the future.