It was Interstellar good; even if the science in The Martian wasn't as hard as it was in Interstellar it was so f-ing close it doesn't matter.
My only real "WTF?" moment was when Matt Damon replaced an airlock with a sheet of plastic, duct tape, and ratchet straps. That sheet of plastic has to hold in a few tons of air pressure, and unless it's some kind of miracle plastic--which is not entirely beyond the pale considering this is set in the 2030s--I have my doubts about it holding up. A little exposition on that point would have helped.
But that's one flaw--one!--in a 2.5 hour movie. Otherwise? It was damned tightly written, obeyed the laws of physics, and didn't play any games. I loved it so much I found myself looking at the extras on the disk, not wanting the adventure to be over, not wanting to leave the characters yet. They're all the kind of people you want to spend a lot of time with.
Next step: getting the book. I'm betting it'll be worth every penny, too.
The Martian, five stars out of four. (Interstellar rated just as highly.)