In summary, the best he's ever written. In addition to making good use of neat techno-gadgets, it's got a good, coherent plot, with a beginning and middle that lead logically to the end. Plus it has realistic space battles. No faster-than-light stuff, but battles showing relativity effects that take months and years, not sudden blinding laser flashes.
The story first centers around a humanoid (hominid?) alien of the Pak race living near the center of our galaxy. Psspthok's people stop eating when they lose reason to live, and that's his problem. He solves it by finding out about an expedition by his people to the outer arms of the galaxy. It ended in disaster and they called for rescue. He decides to rescue them. Yes, it was three million years ago, but Pak are tough, and the descendants are worth saving. So he comes out to save us. That's right, we are the descendants. But are we going to want to be saved, the way he intends?
Many authors have featured characters, human or alien, with high "IQ"s (a much-misused term, but that's a subject for another day). The challenge to make us believe these critters are really, really smart. Authors don't always succeed in this, of course. But here, Niven succeeds admirably. At one point, upon becoming a protector (at which point, your intelligence increases significantly), the character wakes up thinking, "I've been stupid!" Of course, you retain memory of your former experiences and actions. And with increased intelligence, you can see how you should have done things differently. And Niven says problems become less interesting because you solve them so quickly! That make a lot of sense to me.
In a way, this pervades the book. I say this because when I got to the end, I thought, of course, it HAD to end this way. It just made a whole lot of sense.
Also, I was impressed by his use of physics. At one point, he uses a gravity-field device to make a huge lens, and therefore a huge telescope. What a great idea! You don't have to worry about weight, absorption of the light, or aberrations in the "surface". And you can make it practically as big as you want! Now if only we could actually generate such fields! Moreover, he points out that the exhaust from a fusion drive should have a characteristic signature that one could detect spectroscopically. And then he gets it right! I actually learned some physics from this book. Painlessly, and entertainingly.
To me, this is one of those if-you-only-read-one-book books. That is, if you only ever read one book by Niven, try this one. Or possibly Ringworld.