Basically, it starts off with a guy, waking up from a coma, in a hospital bed. His room has been locked, but he has been kept alive on a drip. The entire hospital is deserted. He manages to get out of the hospital, into the city centre of London, which is completely deserted. He screams at the top of his voice, but no one is there! (This part looks really cool..coz you can see, that it really is london, and it really is deserted! They shot it really early in the morning, and were given permission to cordon off areas of the city. I thought that was really cool)
anyway, it turns out that 28 days before, an epidemic had broken out in london. this disease, Rage, is highly contageous. It turns those who are infected into insanely violent people. Blood contact will cause infection within seconds. Jim eventually meets up with two other "survivors". Not just has the entire country been infected, but the entire world. Its now a game of surviving day by day.
Notice, the word Zombie is never used to describe the infected people. I would strongly reccomend this movie, as it has a lot to offer. It is incredibly brutal at times, yet occasionaly quite tender. It has characters who are very well developed, and interact in a very real way. In the latter half of the film, the story starts to develop in a very unexpected way, which makes for compelling viewing.
The reason I would say that it's not a zombie movie, is that the phrase "Zombie Movie" has certain connatations, most notably; chainsaws, shotguns and flame-throwers

. Instead, this movie is more about the reactions of the characters involved, and about human nature in times of crisis.
EDIT: I should mention that this film is made on quite a low budget. It is shot almost entirely on Mini DV. I don't know why, but that seems to bother people. I have read reviews on IMDB blasting this film, purely on the basis that it was shot on DV! Give me a break! So if this is a problem for you, then go see something else. Personally, I find that low budget films can sometimes come out
better than they would have done with a larger budget. Why? Because on a low budget, you only have to please yourselves. You don't have a bunch of ignorant corporate fucks breathing down your neck, deciding what would or would not make the film more popular with the general public. Result: Slick, ultra-glossy Bland Homogeneous movies, with a beautifully high tech credit sequence! Grrrr....

sorry...got a bit off track there. 28 Days Later Rules!