I won't say it is a pleasant surprise because this is not a “pleasant” films. It is a very good film, but yes, it is dark, very dark. If you are looking for signature Arnold action and catch phrases, look elswhere. If you want to see a film that is well crafted and moving, check out Maggie.
Despite a couple of moments where Arnold tries a little too hard, you can really see him stretching his acting muscles and performing well beyond anything we expected from him. This is not a zombie film, it is a film about a father slowly losing his daughter and trying to cope with it… And with zombies. This is not a horror film and even the gore is kept to a relative minimum.
I am surprised by my statement here, but I actually was impressed by Arnold's performance and you can really see him digging deep into his own experience of fatherhood to pull out that pain and suffering of losing a child to disease, all-be-it zombieism.
If you like the dark and drreariness of movies like The Road, etc. Then check out Maggie, it will surprise you.