Sure, Up From the Depths is a zombie novel. There's the usual hordes of the dead, people trying to survive an event their unprepared for, and so on. Yeah, this is a zombie book, but it's a hell of a lot more than that.
Think of a zombie novel written by Tom Clancy. Think Day By Day Armageddon but with a cast of hundreds and action by the bucket load.
I'm not going to try to summarize the plot here, but suffice it to say that there's a lot of undead, a race to uncover just what the hell is happening, shadowy dealings, and feats of daring do to keep you fired to the page.
The writing is good - there's ample description, good word choice and it's well edited by most reasonable standards. The pacing is good with chunks of action thrown in amongst lengths of exposition a and dialogue. For the eagle eyed, there's plenty of fun little "Easter eggs" thrown in throughout.
Furthermore, Jackson is a veteran and his command of military lingo, acronyms, tactics/SOP is phenomenal. If you're like me and you roll your eyes at the typical zombie novel where a soldier talks about shooting their .22 caliber M16 rifle from the hip, you'll find the authenticity of this book a real breath of fresh air. For the uninitiated (or even the old hand in some cases), there's a beefy glossary in the back to guide you along.
The characters are many and varied though "screen time" depends on the character. Some are funny, some are serious, some are realistic, while style are a little more fantastical. None of them goes beyond the pale in terms of believability and most are very entertaining.
Now for my quibbles. First, the number of characters precludes getting to know a lot of them on a deep level. You may have to keep a pad of paper many to keep the huge cast straight.
Second, this is a series book. Dir some this might be a turn off in and of itself. Otherwise, this book is very much a set up for the rest of the stores. It's a great read, but it can feel like there is a lot of irons in the fire.
But the juice is well worth the squeeze. The series is epic in scope and extremely entertaining. Book 1 is a great set up, and fun to read on it's own, but it also presages a much larger and jaw dropping zombie series.