James Gunn is a successful screenwriter. He wrote the sceenplays for Tromeo and Juliet, The Specials, Scooby Doo, the Dawn of the Dead remake. I'll let you decide where he's had how much artistic success he's had with which on you own.
He makes his feature directorial debut with the new release Slither. A movie that seems not to be doing terribly well at the box office, but really should be. I seriously doubt She's the Man or Stay Alive are anything close to as fun, funny or thrilling.
The movie it seems to be drawing the most comparison's to is Tremors. It's a good comparison and I'm glad people are making it more than obvious splatstick movies like Evil Dead II or Dead Alive. Mind you, it's certainly gorier than Tremors, but it has the same tone of light-hearted but surprisingly well-realized characters wandering somewhat knowingly into the absurd situations of an old monster movie.
It manages to keep the laughs coming, while also staying smart enough to avoid most obvious horror movie clichés. In that, I'd say the previous work of Gunn's it seems most like to me The Specials, a wonderfully charming Superhero movie about every moment in their lives except the Superheroics, in sort of playing the humor from the angle of the unexpected instead of the more obvious mockery of the expected.
I'm probably overselling it at this point. It's not brilliant. It's just surprisingly smart. Mostly, however, it's just a hoot!