No I haven't but I think I have heard of it.

I read it, but I didn't think much of the cliffhanger ending. Cliffies are for the ends of chapters and installments, not the ends of books.

It seemed as though Korman ran out of good ideas. The dragonspy was cliched and impossible, and the "super-polymer" was too deus ex machina. And all that about Marty being "tested" was implausible and silly. 

It really irritated me that Korman put Bronson in disguise for no real reason other that to give us a "surprise". It drove me nuts when Marty would go in and start ordering everyone around, and I wanted to see more of Grace overcoming fears and writing in her Moleskine.

I'm sick of all the environmentalist propaganda that people stuff into their stories, and this one was on the verge of doing just that.

*Clutches head*

I really enjoyed Cryptid Hunters, so I was excited when I heard about Tentacles.  However, it fell way short of my expectations.  It was one of those sequels that felt like a sequel for the sake of a sequel, without any real reason or true plot.  The book seemed endless as well, with a lot of MARTY-MARTY-MARTY-oh, yeah, Grace-MARTY-MARTY-MARTY.  The characters were much flatter than in the first book, and there wasn't nearly as much (if any) gripping suspense.