A lot of that is up to the main character, Astronaut Mark Watney, who is left stranded on Mars when his crew believes him dead. Most of the book is written in the form of logs Watney writes upon finding himself the sole inhabitant of the red planet. Given that, in order to make it to outer space, you need to have a huge base of knowledge (Watney is a botanist and engineer) and he relies on a lot of this knowledge to facilitate his survival, the book in concept runs perilously close to being a dry lecture on how one might conceivably survive on Mars. Watney is written with a goofy charm, though: a quirky sense of humour that lands him just on the good side of "snarky Big Bang Theory character." At one point he has to describe a very wordy unit of measurement, so he chooses to abbreviate it to "pirate-ninja." He's self-effacing and vulnerable, aware of the gravity (haa) of his situation, and sure intimidated by it, but never overwhelmed by its hopelessness. So he becomes a guy we are eager to hear from, root for, and relate to... which it makes it easier to read attentively when he's describing the process of converting oxygen and hydrogen into water, or farming potatoes in the habitat. Why he has potatoes on Mars is one of the bigger leaps the book asks us to take, but is pretty necessary to believe in for the story to happen.
So yes, while there's a lot of hard science in the book (which I can only assume is reasonably accurate) it never drags, never bewilders, never loses the point or falls too in love with the idea with explaining the gadgetry and methodology. It retains forward momentum, and while it doesn't expect its readers to be experts, it doesn't aim itself at idiots either: you picked up a book about a guy surviving on Mars, you're going to learn how this guy survives on Mars, dammit!
The book has an equal reverence for science and human determination - basically the recipe for an astronaut. Like, if you're not into hearing what an awesome bunch of people astronauts are, (crazy bastards to blast into space in giant bombs basically just to look at rocks) - and even ground control gets into the mix - this is decidedly not the book for you. Luckily, as we know now, science is pretty damn cool, and is a favourite subject of a large number of cool people.
Come for the content, stay for the tone. As much as the situation is dire, on a fairly grandiose scale, its view never slips from the very human, eye-level perspective on Watney, and later the people charged with helping to save him. In fact, I'm actually a little disappointed that Ridley Scott picked it up to adapt, with Matt Damon in the lead role, because that feels like they're taking a fun, quirky story and trying to wring a prestige picture out of it (not to mention there's not a ton of action and thrills in the idea of Watney riding a 20 km/h rover for days on end.) The project threatens to unsettle everything that makes the book what it is. It would make a great cult film, though.
I do have some nitpicks of my own, which have nothing to do with the scientific content. I could have done with an Epilogue rather than the novel's somewhat abrupt ending, but that ending is consistent with the concerns of the book. The other nitpick threatens to unravel the whole thing: at one point CNN is described as airing a regular half-hour program called "The Watney Report." In reality, CNN covered the disappearance of Malaysian Airlines Flight 370 around the clock for weeks on end with absolutely no developments to report on, so it's safe to say the entire network would be the Watney Network.