This isn't a bad book at all, but it feels so completely...unnecessary. Xeelee: Redemption (and I presume Vengeance as well) is basically a retelling of his masterpiece Ring which more or less covered the entire Xeelee saga from near future to 5,000,000 AD. Don't get me wrong, the Xeelee stuff is what Baxter is known for and I consider Ring to be one of my favorite Sci Fi books so this sounds good enough on paper...but, Ring didn't have a whole lot that could be or needed to be improved upon, so ultimately we just get most of the same people/events/aliens just told in a different order and given different names. The Ring is now The Wheel. Photino Birds are now Photino Fish, etc. Michael Poole has already done all there is to do in the universe so now here he is doing it all again in a slightly different version of that universe, for some reason--oh and now there are two Michael Pooles because one just isn't enough I guess. That said, if you're not that familiar with Baxter's work than there is quite a bit to like here without the burden of having heard it all before.
My biggest problem with the book is that it feels so...dull. There is almost nothing in the way of conflict or action. For the most part the entire thing is just an observer's perspective - the equivalent of a national geographic documentary on Baxter/Poole's universe. We're taken to a lot of interesting locations, given some description of them, the characters try to understand how/why a thing is the way it is, and then we move on. Rinse, repeat. There is nothing that endears the reader to the characters or events as whole, nothing that makes you feel anything for any of them. This also isn't helped by the dry, functional writing.
That said, there is a lot of legitimately cool stuff that is brought up in the book and if you're not that familiar with the Xeelee Sequence than I'm sure it will be vastly intriguing. The big picture of the Xeelee/Photino Bird conflict is of course mindblowing; the sheer scale of the Ring itself, how it works, what the Xeelee's plan for it is, the discworlds, watching galaxies move (and collide) over millions of years, etc is all insane to contemplate and brilliant. Forcing the reader to expand their mind to think in terms of extremely long timelines is awe-inspiring and one of the best aspects of Baxter's writing. However, the problem is that all this was already done, and done better in Ring. I found the universal conflict to be significantly more impactful in Ring as the Photino Birds were explained in greater depth, the characters were more invested in the events (things of significant consequence were happening TO them, not just AROUND them), and Baxter really nailed the feeling of ultimate despair at the end of the universe when the Ring is destroyed; you don't get that at all here as the focus is more on explaining how the Ring was/is built, how it functions, and then some side stuff about evolution on fabricated Xeelee worlds (don't get me wrong, this is also cool, and fills in some aspects that were not in Ring, but none of it is nearly as impactful). As for the Photino birds, they feel like an afterthought and are only briefly mentioned. The crew make a point to keep a stored Photino Bird with them for basically the entire book, and I can't even remember if they actually did anything with it or not.
One of my favorite aspects of Baxter is his ability to write compelling and truly alien-feeling alien races. The only race we meet here is the Ghosts, which I definitely enjoyed-- the Ghost planet is the most exciting part of the book. But much to its detriment, the other pivotal alien races from Ring: the Squeem, the Qax, and their Spline warships, are all but completely left out. We do finally get to meet an actual Xeelee though which is great, although the encounter is extremely brief and largely insignificant.
One big positive about this book is that Baxter has refined his ability to portray his scientific genius. In the past he tended to blind the reader with science-- either extremely hard-to-conceptualize abstract descriptions like in Flux (not to mention the straight-from-textbook style infodump), or long-winded, jargon-filled passages like the entire chapter in Ring describing how the Sun works. As per usual, there is plenty of science here, but it doesn't feel forced, overdone, heavy-handed, or unnecessarily abstract. It's clear that Baxter put significant effort into providing accurate, if theoretical, explanations for how things would work.
Overall, this is an adequate return to the Xeelee universe, though in myriad ways it feels like Baxter's Greatest Hits: a bunch of stuff from his other books cobbled together which has little to set it apart or above any of his other work. Not a terrible place to start, or to check out if you've read some of his other work, but not the best. Regardless, definitely check out Ring because it's basically the same story but superior in almost every way.