Suffice to say Garrett's commando doesn't do a great job of transporting that nasty assassin. (And don't even ask why this super-valuable prisoner is being transported via boat and not by plane; the explanation is too absurd, even for a movie this willfully absurd.) Like any smart villain trapped on a boat in a delightfully unhinged B-movie, this one fakes a seizure, dispatches several armed soldiers, and heads deep into the bowels of the vessel, where he decides to let all the wild animal loose in an effort to distract and annoy his pursuers. The mid-section of Primal is where you'll find the most amount of fun: that's when the wildly tenacious assassin dispatches a small army while a few unfortunate side characters stumble across some very aggressive reptiles and primates.
The real problem here is that Primal, despite its wild premise and game cast, never really cuts loose with the insane B-movie action-/bio-horror mash-up that the those assets seem to indicate. In other words, the flick is a little too serious for its own good. Cage, being Cage, offers a bit of offbeat wit and some unpredictable character beats here and there, but Primal doesn't give the man enough opportunities to find the weirdness in his mostly one-note hero caricature. The majority of the welcome weirdness comes from Durand's frequently maniacal performance, the ease with which this one skinny lunatic disrupts an entire boat full of armed men and women, and the too-few moments in which the angry wildlife pops up and adds a fun little wrinkle to a nicely shot but otherwise very standard action flick.
If you dig Cage, Die Hard-inspired action flicks, or any story that could be described as "when animals attack!" then you'll have some fun with Primal. But given all its legitimately appealing credentials and a solid ensemble cast, Primal simply refuses to dive into the wackiness of the premise, and a generally straight-faced presentation is not what most people want from a movie that features Nicolas Cage, Famke Janssen, a homicidal maniac, and a bunch of wild animals on a boat.