I loved reading The Martian online even in the inherently somewhat annoying written in realtime form; so much I showed up to get a signed copy when it was released.

In general I'm a sucker for hard scifi, but much of the state of the art in that space is often inaccessible to those of my friends that aren't deeply versed in the literature. The Martian is both accessible (at least to an audience which is generally okay with science and technology) and compelling story telling as well.