I picked up the original "Meg" novel a couple of years ago and found it a pleasant surprise. It was well written and hit the balance perfectly between being believable and having some fun, over the top action. It was refreshing to find a giant sea monster story that didn't have the usual radiation/mutation/government experiment origins and was coupled with some likable characters. I enjoyed the sequel but as I've gone through the series there's been a noticeable decline in the quality. I was hoping "Nightstalkers" would end that trend but was sadly disappointed.
I understand that five books into a series there's going to be some rehashing of similar plot devices but I couldn't help feeling that I'd already read this book. It's been the same for a while now - despite tragedy after tragedy inflicted on the Taylor family by these sharks, they insist on repeating their mistakes. Initially they want to destroy the sharks, but then decide they want to save them and imprison them back in the lagoon/aquarium one more time despite all the failures of previous attempts and countless deaths. The megs are the secondary antagonists at this point, playing second fiddle to some even larger creatures, but the formula is still the same.
By far the worst point of the book is about 75% in where a character is introduced and brings with him an absolutely ludicrous alternate reality/time travel subplot. Yes you read that right, TIME TRAVEL!!. I wish I was making this up. It feels ridiculously out of place and is dropped after a few chapters never to be mentioned again (thankfully). I later discovered that this was a crossover with another series by the same author, and it feels like a cheap ploy to generate sales of his other books. At this point I actually put the book aside for a few weeks feeling like it wasn't even worth the effort but I'd already invested enough to want to see it through to the end. I won't spoil anything, but the door was left open for more sequels to follow.
If you've read the first couple of books of the series then please just stop there. It's sad how terrible this getting.