The most important thing one should know about this film is: "Nekrotonic" is a truly guilty pleasure for anyone who's into gunfirghts, gore and flat jokes. Now, let's elaborate this by numbers.
This is a second work of Kiah Roache-Turner ("Wyrmwood"), and most of his style also appears here. That means - lots of action, decent amount of blood and guts, comic-style characters, and cheesy dialogues. The good news is all of this works good in this kind of movie.
The basic concept (Nekromancers vs. Demons) looks like "Ghostbusters", but with an R-rating. There's also references to horror classics (such as "Hellraiser" and "Exorcist"), but not much. The acting is not the most attractive side of this film (Monica Bellucci is clearly overacting, but I'm sure that's the point here), so just foeget about it. Enjoy the little things. Like old-fashioned SFX (less CGI, more good prosthetics), pretty girls with guns, and good soundtrack. I mean - where else you can see slime-covered badass girl killing demon-possessed people with "Can't Take My Eyes Off You" by wonderful Andy Williams on the background?
Yes, zero character development. Yes, really bad jokes. But if you're looking for a bloody and fast-paced mix of a horror, action and comedy - you're on the right way.