The subtitles are really kept to a minimum Brian. I can see why some people get irked by subtitles, but in this instance I think if the cast had spoken English it would have lacked the authenticity it has - the actors all spoke in the actual old Mayan language which must have been some undertaking!
I don't think the subtitles will bother you - the film is something truly different, and the closing sequences are just edge-of-the seat suspense - you can't help getting involved.
Give it a watch and tell me the head honcho of the bad guys isn't the scariest Mofo you've ever seen!