This review will contain spoilers!
In many sentences:
It's probably a good thing that "The Dark Tower" never made it to publication in its current form. As it is, it doesn't quite fit in with the other books in the Space Trilogy, either in concept or in execution. Perhaps this would have changed upon final publication, or just as the story progressed, but as it is (and that's all I can comment on) it doesn't feel like a Space Trilogy book. One of the things that makes me say this is the lack of presence (in terms of the affect he has on other characters as well as on the reader) of Ransom. He is more of a side character than the focal point the way he is in the other Space Trilogy books.
Another, weaker aspect of this book for me was the narrator's asides. While there is some of this in the other books, it almost felt like Lewis himself didn't quite know where he was going with this story, and so these were put in there to help him move the story forward while he figured it out. Considering he never finished (or at least not that we know of) it, this may not be too far from the truth.
With the few complaints I had about the story aside, overall I really enjoyed it. All the time stuff was fascinating. In fact, I wish someone had "completed" the story since Lewis never got around to. Yes, it wouldn't be Lewis so it wouldn't be the same, but independently of anything else the concept itself is quite engrossing.
"The Man Born Blind" is short, but powerful. It's great the way it turns an idea as simple as light on its head, and reveals that it's not at all something we ever think about or could describe if it came down to it. And here is this poor blind man, always hearing about light his whole life, only to believe his operation has failed when he can see again because no one can show him what light actually is. It's heartbreaking to envision him, afraid to ask again about the light his wife is talking about, but unable to think about anything else. You can almost sympathize with his decision to throw himself into the gulley when he finally sees light for the first time. Like with Joyce's short stories, it's amazing how much Lewis is able to capture all of these elements within just a few pages.
Overall, this is a really cool piece of history for fans of Lewis. This is not, however, the first place someone should head if they are just getting introduced to his works. It would be like reading Unfinished Tales or The Silmarilliion before picking up The Lord of the Rings