I felt inclined to write a review due to the poor ratings that the book has received so far. While it isn't as good as his other well known books (namely The Forever's), Marsbound is still very enjoyable and very easy to read, and as with his other books his writing style makes you turn page after page.
The plot does have a twist quite early on which may seem strange when it is first read, and it is fair to say that it takes a bit of imagination to accept it, but Joe Halderman isn't known for hard science fiction; he is a story teller, and tells this story very well.
Don't be put off by the other reviews. The book travels at a great pace, is fun to read and let's be honest, even a bad book by Halderman is better than most.