Better than a sharp stick in the eye, but not as good as a the worst Heinlein book (by which I mean Number of the Beast, not the Stinkeroos).
It is well that Robinson does not purport to have created a Heinlein novel. There were too many swears, for one thing, which I thought needlessly disrupted the Heinleinian feel. (I'm not opposed to swearing, but one simply does not picture a Heinlein character uttering an oath stronger than, "bushwah!" or, in great extremity, "damn it all!") And too much of the main character staggering about in an altered state of one form or another. There is also a bit too much fanboyish shouting out to the Future History, also. (But I hate winky Fan in-jokes in general.)
However, Robinson definitely does tap into the alchemy that makes for a clever and engrossing Heinlein book, and he doesn't do such an awful job of cobbling together an ending.