The thing you need to know going into this is: It's a big story. I don't mean long; I mean big. If you expect to be presented with characters whose heads you can get into, whose individual stories you can get involved with, this book is likely to disappoint you. It isn't the story of a single character, or even a small group. It's the story of a civilization developing almost from scratch.
How much from scratch? It goes like this: The Gerns have attacked Earth. A shipload of humans flees in the direction of a planet called Athena, whose resources are humanity's last hope for survival. In transit, they are intercepted by the Gerns. Those with skills useful to their new overlords are taken as slaves; four thousand men, women, and children deemed useless are dumped on a planet called Ragnarok with minimal supplies to sustain them. Ragnarok boasts a gravity 1.5 times Earth's, a binary star system that gives the planet a weather cycle swinging back and forth between extreme heat and extreme cold, no significant deposits of metals or minerals which could be used to build helpful things like spaceships or weapons, a "hell fever" that kills overnight, and at least three species of animals intent on killing these new interlopers. Also, it's the beginning of winter, and the Gerns don't provide the humans with niceties like shelter. This is intended to be an execution.
It's rough. It's really rough. Four thousand dwindle to under a hundred in the space of a few years and the humans are reduced to near stone-age levels of civilization. But the scant handful of survivors are just that -- survivors. And they hate the Gerns with a blazing passion that drives them to take the only practical view of their situation: the long term. They expect the Gerns to return, in fact actively work to lure them back, and the intervening time is not spent in idleness. Knowledge is preserved until it can be useful again, each new generation is better adapted to Ragnarok, and the humans begin to claw their way back up out of the abyss into which they have been thrown.
In broad terms, I liked it as long as I could look at it in the appropriate context. I warn my readers about the nature of the story not to drive them away, but because I did not understand it at first and found myself disliking the story for the personal details it skipped, the continual killing off of what seemed to be main characters, the appalling madonna complex all the female characters seemed to have (product of the '50's? yes indeedy), and the rather simplistic nature of the basic overarching plot. I think it was after the fourth or fifth viewpoint character died, though, that I started to get it. This is not a story about Irene, or Bill, or any of their descendants. It isn't even really the story of a scrappy band of humans triumphing over cruel alien invaders. It's about what happens when you dump a bunch of people on a planet with everything against them and no resources, and they have to be tough and innovative and yet also cooperative to survive. And most of all, they have to think not just of their own survival, but of how their actions can allow future generations to survive even longer, how they can ensure freedom for their great-great-grandchildren if they can't get it for themselves. It's never about the character you're looking at, it's about the next generation, and the one after that, and the one after that. As long as you look at it like that, it's a fairly interesting little thought-experiment.
It does have some serious faults. There are times when things seem almost a little too easy -- which is quite a feat given what the humans are up against. Time seems to have stood still outside of the immediate scope of Ragnarok while all this evolution was going on. There are places where a spouse, a child, a relative, a friend springs up seemingly from nowhere and even if this character's life isn't the point it might have been nice to have a teeny bit of background slipped in. There are things about Ragnarok itself that don't quite make sense to me. Theoretical knowledge of things no one has seen or done for generations seems to transmit remarkably well to practical skill. And really, honestly, no one does seem to have given much thought to what happens after this story is over, which... For people who spend generations plotting their escape, seems a little short-sighted.
In a weird sort of way, though, this almost complements the story itself. The humans dropped on Ragnarok have had to put aside everything that wasn't relevant to their project of surviving long enough to get off the planet again. Given that they are required to maintain a certain level of theoretical knowledge in order to have any hope of success, even if things like operating a blaster and flying a Gern cruiser are beyond their actual technical capabilities, what gets kept is sort of eclectic and might not appear to make sense if you don't have a good feel for their goals and methods. Likewise, Godwin has neglected everything that wasn't directly relevant to the core concept of this group of people starting from the bottom and working their way back up through the layers of civilization. The point is to have hostile species on the planet, not to explain said species' motivations; the point is that there is another generation, not the story of its conception; the point is how these people rise from the depths, not what they see or where they go when they return to the heights. The point is that the struggle exists and where it goes, not to detail every last movement of the battle.
In that respect, I'd call this work successful. I'd certainly recommend it to anyone who's looking for a good piece of broad-scope old-school sci-fi. The arc is very different from that of most fiction we're used to, and that does take a little effort to assimilate, but it's well worth it.