Nothing wrong with this book as such, it was just a bit boring, and nowhere near as good as Day of the Triffids. For me the enjoyment was limited by the fact that we don't get to hear much about the aliens - there's no description of what they look like (the closest we get are their 'sea-tanks', and it's not clear if these are the aliens themselves or a transport mechanism or an autonomous vehicle), what their motives are, whether they want to eliminate humanity or would consider a peaceful co-existence etc.