Way back in the 1970's, Larry Niven established himself as one of, if not the, premier author of gosh-wow Big Ideas in science fiction. His greatest achievement was the Ringworld, a hoop a million miles wide and the size of Earth's orbit around a Sol-like sun. He returned to the world with a couple of sequels over the next couple of decades, which as I recall (and as I recall other people's opinions) weren't very good. Now he's returned to Ringworld one more time, and this time it is an impressive trip. There are new Ringworld-scale ideas, and so much stuff happens, packed into a rather short book, that (having just finished the book) my mind feels a bit like a pinball that just drained after setting the high score on a very fast machine. There are so many bizarre plot twists that it's hard to get a handle on the plot at all. There are some real problems with the story; the situation that drives the main action in the story seems rather contrived, and a bit of diplomacy would seem to be a more likely way to get out of the mess, if it got that far, than the main event in the story.
But on the whole, it was a fun ride. This is the Larry Niven who was my favorite author when I got started in SF, the Larry Niven we've seen very little of lately. It's not a perfect book, but it's got the right feel. 8 out of 10.