Last movie I watched in a theater was "The Hunt for Red October"
Book are better than movies, IMHO.
The last movie I watched in the theatre (as far as sci-fi and having already read the book goes) was Carl Sagan's
"Contact".
WARNING: HEREAFTER BE SPOILERS!!!While it varied from the book in a few important (and some not so important) aspects, I was satisfied enough that Robert Zemeckis got it as close as he could have without some naff background explanations. For example, the
"message hidden in the value of pi*" would have been a very difficult concept to get across to the public in a film (it was hard enough getting it across in the book) because it implies that the aliens were not only ancient, but that they created the physical laws of the universe, and therefore, the universe itself.
ETA: Just thinking about that, I still think that for the most part, movie directors, producers and studio executives often seriously underestimate the movie going public's capacity to understand complicated concepts.
Blade Runner (based on Philip K. Dick's superb
"Do Androids Dream of Electri Sheep") is a great example of where studio executives interfered in a movie in an effort to dumb it down, only for their interference to have the opposite effect.