How close it is to the actual book?

In terms of the action portrayed it's mostly pretty close to the book, but in terms of the overall tone, it is IMO drastically different: In my opinion, this movie in tone & effect has much more to do with the 1960s than it does to Fielding's novel.

One example: In the novel Tom Jones is the epitome of a gentleman in all his behavior toward ladies, & would never do or say many of the things that we see from Albert Finney in the film (such as saying that Black George Seagrim has lots of "hungry daughters," with a wink at the audience): The scene in the movie where Tom jumps up to fight the English soldier, because the soldier had kidded about Sophie Western's virtue, is one of the few places in the movie where he behaves like the Tom Jones of the novel.

The style of humor in the movie IMO is much more broad & uproarious, while the humor in the novel (woven in throughout the narrative) tends much more subtle & ironic in effect, though there are some delightfully uproarious scenes.

And there're more points I could make (which I might do later, when I have a little more time to write).


EDIT: You know, now that I have finished the book (I was about 80% or 90% of the way through it when I made this post initially), I have to say that I now consider this movie--in terms of its tone & message--to be a real travesty of the book: I really hate this movie now!