The acting in this film is surprisingly pretty good. Sure, it's not Shakespeare, but the thespians on screen never seem to stumble or fake it. They all do pretty good with their lines. No one particularly stands out, bad or good. Even the girl with the ridiculously phoney accent does a pretty good job.
Nobody ever hams it up.
They don't have to. The special effects in the film, the gore, is also pretty good, if you like that kinda thing. There's buckets of blood and lotsa chewing on body parts nee raw meat. The zombies look pretty cool and there are some interesting ideas going on here. One guy gets attacked by zombies while he's in the water.