I too loved the book (one of the best hard sf books of the last decade IMHO) and thought the movie adaptation was superb. It felt super-condensed of course, but that's to be expected for a Hollywood film and I think they did a great job job translating it to the screen. Ridley Scott has made a lot of average films over the last decade but this is a massive return to form for him. I'd go as far as saying it's his best film since Alien.
I'm not usually a huge fan of 3D but in the case of this film I'd call it borderline essential for the best possible experience. The sense of depth and scale on Mars was superb and I never felt that the 3D was gratuitous, distracting or overdone like it clearly is in so many other films. Some very clever use of 3D layers to convey terrain, dust, HUDs and other onscreen information like character names too.
The book will always be superior of course, but I found the movie to be the best possible experience I could have hopped for. I really hope this is a sign that Hollywood are willing to embrace more science-based titles as getting that mix of scientific realism and action blended just right (without alienating or boring a 21st century audience) is a tricky combo that they pulled off masterfully. About the only other sf film that has come close in recent years was Gravity, but as visually and aurally amazing as Gravity was it was obviously full of a lot of silliness, and groan-worthy dialogue (and is miles behind The Martian in terms of feeling like "real sf"). Apart from a lot of things going right, there's very little in The Martian that doesn't feel believable (well, apart from one major but highly-necessary plot point at the start which I won't spoil for other readers ).