I own the book and have mixed feelings about it. It isn't a horrible textbook. But it also wouldn't be in my top five STEM textbooks. It is mediocre as a pedagogical tool.
It is huge and quite loosely organized, almost as a collection of mini-textbooks rather than one coherent textbook, with the understanding that most courses in the subject would only teach some of the subjects that chapters in it make available. It also begins with quite a few chapters of the more advanced mathematical background needed to do the physics in the textbook, which is convenient if you don't have that background, since you don't have to get math textbooks too. But the treatment of those mathematical topics is basically limited to GR applications of those mathematical tools.
In some places, the wording feels sloppy when greater precision is called for. Some of it would come across well enough in (or in support of) a spoken lecture, with room to ask questions, but it is less optimal for self-study. It makes no effort to be elegant or efficient in expression, preferring a sort of brute force muddling through teaching style. If you want elegant prose, read
Feynman's lectures on gravitation, which are roughly contemporaneous, more easily available for free, and much more elegantly put (but less useful for learning the nuts and bolts of GR).
The basics of GR haven't changed all that much since the 1970s. But I would agree that the chapters identified in post #2 are outdated. It has some anachronistic statements here and there, but they don't really detract much from the substance of most of the topics covered.
On the other hand, I recently bought James Binney and Scott Tremaine,
Galactic Dynamics (Second Edition 2008), which is a natural successor to "Gravitation" applying GR to galaxies at roughly a master's degree program in astrophysics level. And, while Binney and Tremaine is, IMHO, on the whole better written and is more coherently a single textbook, and is slimmer (and more up to date on the subjects it covers which were updated in 2008 rather than the 1970s), it is in tiny, maybe 8-9 point font, and has fewer illustrations and white space to break up the text, so it is quite hard on the eyes to read and slow going. (Perhaps this observation is just my age and bifocals showing.)
"Gravitation" at least has very readable typesetting and a reasonably sized font with plenty of white space and does a better job of breaking up its text with illustrations, in its favor. This is not irrelevant in a textbook that has the equivalent of two or three semesters of 400/500 level college physics class material in it, that you will spend a lot of time working with if you use all or most of it.