I'm amazed the plane held together
That's a Grumman for you...

Not being seaplane-rated, I may be talking out of school, but I think just as with any "bush" landing, a low pass to reconnoiter the landing zone would have made all the difference. Things weren't so bad until he was surprised by the power lines, then it looks like he kept the power in to try to get off again, but there wasn't sufficient directional control. To play armchair quarterback some more, I gottas say if it had been me, I would've chopped the throttles at that point and tried to let her run aground as slow and straight as I could.
I guess if it hadn't been someone as experienced as Gibson (Shuttle pilot and holder of time-to-climb records, etc.), it might have turned out much worse.