It's also not scary. That's not to say it's meant to be, but some real quality horror could've made up for what the hit-and-miss comedy was lacking. As is, there are plenty of the normal horror facets (blood, guts, violence, a genetically enhanced retard version of Lamb Chop, etc.), but it never amounts to anything more than goofy B-movie fun. Although to be fair, when that goofy B-movie fun involves people being ripped apart by mutated sheep, you can't really complain too much. (But that doesn't mean I'm going to stop.)
As a rule, horror filmmakers should always make sure their surviving characters are likable enough that people will care when they survive. The people behind BLACK SHEEP did not follow this unspoken rule, and in turn the film's biggest flaw was born... The characters are annoying. The ideas behind the characters are very funny (the central protagonist has ovinophobia - an irrational fear of sheep, while the love interest is a spiritual vegetarian hippy), but the way those ideas are handled are not.
If you don't care about any of these problems, and only care about seeing a hilarious one-joke premise about killer sheep being stretched to its limits, then you'll probably enjoy yourself. The actual gore and make-up effects are all handled extremely well (props goes to WETA for that!), so those looking for some quality sheep violence won't be disappointed. Those looking for a witty script and imaginative direction, however, will be.
Audio Commentary (with writer/director Jonathan Kring and actor Nathan Meister): A fun, informative discussion about the ins-and-outs of the film. Exactly what you'd hope for when listening to something like this.
The Making of Black Sheep (31:29): An extremely worthwhile look at the making of the film, showing all the work that went into creating the effects, doing the stunts, and so on.
Deleted Scenes (3:38 - with optional commentary): A few cut segments have made their way here, many of them featuring gags fans should find amusing.
Blooper Reel (2:26): The usual line flubs and goofs. Amusing, but nothing you haven't seen before.
Early Morning (0:32): This extremely short "surprise scene shot exclusively for DVD" is nothing more than an humorous throwaway gag.
Also included is the film's Trailer.