This will be a shorter post, with less detail, since Niven and Pournelle's Footfall is a selection for my book group.
There was a time when move-goers and readers looked for vast far-flung disaster epics, like The Poseidon Adventure, Towering Inferno, and Lucifer's Hammer, with a cast of thousands and multiple storylines to offer as many views as possible of the events of the story. Written in 1985, Footfall is a natural extension of that process, marrying up the classic alien invasion story to the disaster epic. The Earth, with the Berlin Wall still standing and US/USSR relations as chilly as they would ever be, finds itself the target of an invasion force. Of course, one of the impediments to resisting the aliens (who call themselves the Fithp) is that Earth is so divided, not only along politico-economic lines, but also along national lines. So at first the aliens find Earth to be an easy target.
But Niven and Pournelle load the dice in favor of humanity: the Fithp did not happen along their technology on their own; it was handed down to them by a predecessor race that has disappeared but whom the Fithp revere as gods. What this means is that, while the Fithp are technically more advanced than Earth, they are not innovative or creative; they are just tool-users with better tools. They are also herd animals, with instincts for the survival of the group is fairly malleable. While they intend for humans to eventually become part of t heir culture, as they invade, some Fithp end up separated from their fellows and when found by humans, they start to bond with them, passing on the "secrets" of the Fithp. The Fithp, as a very young race with little experience and creativity, expect humans to act just like the Fithp; but humans quash their instinct to expect the Fithp to act terrestrial and thus are able to take advantage of any cultural weaknesses. Furthermore, the FIthp came to Earth with no way to retreat should they meet a superior race—they would either conquer or join the race they find. Such a lack of caution doesn't seem like a useful trait for a space-faring race—retreat should always be an option. So when the Fithp are ultimately presented with their infal dilemma, they have very little choice, based in good part on incredibly poor planning.
Footfall is also extremely dated. While tensions between Russia and the US are heating back up (cooling down?) now, they are not nearly as chilly as the mid-80s. Also, one of the primary vehicles in the human resistance fleet is the space shuttle, a way cool toy for the mid-80s but well past its prime today. It's quite jarring to find the Challenger on a suicide mission when it attacks the Fithp mother ship. The first half of the book is filled with allusions and settings that have little to do with the world we know today, but once the Fithp attack, those ideological and temporal differences are not nearly so evident.
All in all, Footfall, though in hindsight perhaps not so deserving of its award nominations. It's a fast-moving adventure with all of humanity at stake. Niven and Pournelle capture the voices of their characters extremely well, bringing the global disaster into a more personal light, which was always the point of the disaster epic anyway. It's appropriate that I was led to this book at this time of year: it makes for perfect beach/airplane reading.