Millennium is one of my favourite books. I happened to see the film recently and here was my review:

In the category of time travel romance with end of the world movies this sits near the top.

If you've read the book you'll realise that a great deal has been left out, most notably the BC character which is a shame. However the titles said the film (1989) was based off the short story "Air Raid" published 1977 rather than the book "Millennium" published 1983.

Anyway, if you can get past the hokey 80s special effects, enough like the book to be enjoyable.

If you haven't read the book you probably won't have any idea what is going on despite the characters attempting to explain it to each other as the plot isn't explained well at all!