We had a good look at the first 28 minutes of this movie a few weeks ago, and it definitely held up to our expectations. There's certainly a lot more gore here than in the first film (and the rest of the movie is a lot bloodier than the first 28 minutes), and there were quite a few pop-out-of-your-seat moments throughout, as evidenced by the number of times that my rear end left the seat. Just to prove I'm not particularly susceptible, the people around me all leapt at the appropriate moments as well.
28 Weeks Later isn't so much a sequel in action as it is in spirit. It is literally 28 weeks after the breakout of the rage virus, and the population of mainland Britain has been wiped out and the country has been declared safe and an America led NATO force is responsible for repopulating the city of London. They've re-established water and power, have operating public transportation, and apparently even the taps are flowing at a local pub that has been re-opened. It's been declared good enough to allow 15,000 people to start repopulating the country, and that number is growing with every new arrival.