So, for the first half hour, roughly, I could have thought that "Doomsday" was much like "I Am Legend" or some other such movie--the big bad of the movie is actually a microbe, and while this one doesn't mutate people or turn them into zombies, it does kill them in a quick and painful way. All of Scotland is infected and cut off from the outside world, and many years go by as the disease burns through the population. Then the disease shows up in an overcrowded London, and a small group of military personnel are sent into the quarantine zone to look for a possible cure.
It is all done well--tense, intense, stark, with some action. The main heroine is one of the last to get out of the quarantine zone before it is permanently closed. In the escape, she lost an eye (and the fake eye is quite a clever idea). Roughly thirty years have gone by when the main events begin, and she is some kind of paramilitary or law enforcment officer.
Then she's recruited to lead the group into the quarantine zone, and of course things go wrong right from the first.
They run over a cow.
Then, they are attacked by punk fulbol hulligan cannibals. There, they encounter a psycho leader and the latest in demented entertainment.
Then, when they get away from them, our heroes (or those left) they are taken by knights on horses to a medieval castle, where they experience ritual purification branding and gladiatorial combat.
Finally, it ends with a chase scene involving a very nice roadster which is somehow not able to outrun the 'customized', and badly so, vehicles of the hooligans.
I have to admit, the movie threw more then a few surprises at me. I was not expecting to have to deal with punks and goths and their idea of "theater". But that wasn't really too much of a stretch, though I do think that a society that been cut off from the rest of the world for about 30 years and had only just survived a very nasty virus would not be going punk any time soon. But that's just me.
But when they brought in the guy in armor on a charger, I think I started laughing. That was not expecting. Then when they showed a whole small group of people in a castle living like something from King Arthur, well, what can really be said about it.
For all of it's cleverness, though, or at least it's willingness to mix genres into a barely coherent mess, I'm not sure I can recommend it. At the least, it's not for the weak. There is quite a bit in it that could be considered offensive. The lifestyle of the cannibal hooligans is, shall we say, completely amoral. The medievals have fallen into a 'pure blood' mindset. There is plenty of cussing and no small amount of gore.
It is a matter for each person whether to see it or not. Frankly, there is not great message to it, so you're not missing anything by not seeing it. But to each his or her own, it is a matter of conscience.