Splice is a reckless monster film that hearkens back to some classic horror movies, like Frankenstein and Eraserhead, but it never quite feels comfortable enough with itself to drop the influences and pioneer something original. It's mostly these influences that make critics call it "horror" in the first place, since it's shot more like a thriller anyway. Behind the shock and novelty of two scientists creating a brand new species which (spoiler!) gets out of control, Splice is just a monster movie.
Two brilliant scientists Clive Nicoli (Adrien Brody) and Elsa Kast (Sarah Polley) run a genetic engineering lab which has extracted the DNA of various species and placed it into two hybrids named Fred and Ginger. Fred and Ginger are hardly dancers, but more like amorphous blobs with indiscernible body parts and a sluggish way of moving. Fred and Ginger are, however, Clive and Elsa's meal ticket to bigger and better projects, such as the creation of Dren ("Nerd" backwards, the anagrammatic name of their employer). Dren is the ultimate hybrid, combining numerous valuable types of DNA (agility, dexterity, and so forth), which the capability and intelligence of a human being.
Dren, naturally, becomes too much to handle in the NERD labs, so the couple moves her out to a barn abandoned by Elsa's old family. Once Dren gets there, some subplots are revealed but never fully enumerated. Elsa is touchy about her family life, but we don't know why; Dren becomes the daughter that Clive and Elsa never had, but we don't know why. We aren't even given the proper tools to figure it all out.
The last twenty minutes of the movie is pretty shocking, but doesn't really redeem the first eighty. I'm not saying it's a bad movie, but it's an uncomfortable amalgam of influences, style, and really quite poor script-writing. But hey, if you love monster movies, you should get a ticket and go.