This is the big one, the legendary series where British comics writer extraordinaire Warren Ellis savagely killed off the superhero team he had single-handedly revitalised just (we later discovered) to clear the way for the introduction of his new, stunning Authority series.
Stormwatch are the UN's superhero crisis intervention team, based on board the Skywatch platform, a large space station in Earth orbit. The team had been used to battling traditional supervillains, but Ellis's time as a writer more often saw them playing a war of nerves against clandestine American government projects to develop superhuman armies, or reluctantly foiling dastardly schemes to use super-technologies to make the Earth a utopia.
Stormwatch: Final Orbit finally sees the Stormwatch team completely out of their depth when Skywatch is infested with Aliens (as seen in Alien, Aliens, Alien3 et al). Another 'super-group', the WildC.A.T.S., teleport up to Skywatch to see what has happened, but they're caught in the same sticky web as Stormwatch and have to try and fight their way off the station.
The shock value of seeing some fairly well established superheroes really, actually die aside, Final Orbit is a pretty disappointing read. It's a slim volume compared to previous collections, the artwork is nothing special, and even Ellis's normally tight scripting can't raise the necessary tension to make this the genuinely moving swansong it could have been. Telling the Stormwatch story through the (unfamiliar to me) WildC.A.T.S. team is a mildly interesting exercise, but the death of the Stormwatch team could have been better told from their own point of view. Doing it through unknown characters seemed a mistaken exercise in narrative restraint.
I got the impression that Ellis had exhausted Stormwatch and just wanted it out of the way so that he could move on. The sequences at the end of Final Orbit that are by far the best parts of the book (added for this collection, I assume, because they're drawn by Bryan Hitch who would later draw The Authority), they read like "housekeeping" epilogues, tidying things up for the continuation of the wider story in The Authority.
If you've read and enjoyed the earlier Stormwatches and the later Authoritys then you'll probably want to read Final Orbit for closure's sake; if you haven't then this won't appeal to you at all, and nor, sadly, does it showcase Ellis's undoubted talents sufficiently to garner him deserved new readers.