I’ve just finished this - hugely enjoyable. I agree with your review. I think the sarcasm was on the edge of being overdone and might have been better if it had been restricted to Watney himself. As for the ending, I cannot imagine how the author could have done it differently. I guess that’s why I don’t write novels. My only quibble with the ending is that it came too soon.
Until The Martian I had been reading a lot of non-fiction. I’m now going to have to go back through this thread a bit to find something that will make equally good commute fodder.