Clark does a pretty good job of maintaining the style of John Wyndham - it's not difficult to go straight from Wyndham's The Day of the Triffids to Night of the Triffids.
There are a few anachronisms - surprisingly more than in the original book, which you'd expect to be more dated. How on Earth can a Post-apocalyptic society, which doesn't even have a stable energy supply, develop reproductive technology that's not only decades ahead of what was possible at the time of Day of the Triffids, but ahead of what's possible in 2011?
The science is pretty sketchy: evolution is Lamarckian, rather than Darwinian; and fertility drugs lead to identical twins, triplets, etc; but on the whole it's a well-written sequel and an engaging story.