As with part 2 of this series, it just wasn't that good. Maybe a little better than part 2, which in retrospect I'll demote to 2 out of 4 stars, and give this one a 2 also. Again, the acting and effects were top-notch, but there was too much extra tacked on to bring things to the studio-demanded three movies. "... thin, sort of stretched, like butter scraped over too much bread."
Let The Martian be your guide moviemakers: If you're starting with a well-known, well-regarded book, you'll probably make more money if you stay faithful to story. Worked for LoTR, Harry Potter, and many others. In contrast look at the film adaptations of I, Robot, World War Z, Starship Troopers, and the like. Sure, they made some money, they didn't turn out to be juggernauts with decades-long sales tails like their source material.