I saw 28 weeks later and enjoyed it, it was pretty good. The opening sequence was excellent, really excellent. Well shot, brilliant cinematography and tone.
However, I couldn't help but sense it lost it a bit with the nato/yanky control territory and there was a prolonged period of silliness, before some more enjoyment came.
If it would have been able to sustain the beginning of the movie, and I think it could have done by not having all the american/nato crap and done a survival thing instead.
i'll leave it at that to avoid spoilers, I think it could have been a lot better and if it would have sustained the excellent opening tone and scenes it would have been a truely great horror film. It didn't though, which is a crying shame.
At least it had the happy ending.