Really loosely based. A fur trapper called Hugh Glass was left for dead in the woods after a bear attack. All the rest is fiction. Great film though.
He also did try to find and kill the men who left him.
though he was unsuccessful, as they managed to enlist (what Fitzgerald was attempting to do)
I'm not suggesting the whole thing is real. But to say it is predictable when it is sticking to an actual story is a bit unfair.