No pun intended - if there is one snake ... there are more. And it is already more than one snake. Monster movies seem to come back in style. Not that I would argue they have a great quality. But they can be fun - Snakes on a train and all that. Well just one section of the movie.
The effects are ok, though do not expect this to have big budget CGI in it. This is a horror movie and the effects are quite obvious. Just roll with it - take it for what it is. Also there are other monsters here too - so not just the (fake/computer) snakes ... but also bats and other animals. Also this has a pathos level that may annoy you ... sacrifices and some cliche character turns make this ... well make this what it is ... like it or not.