I liked that the opening was vague and confusing. I thought it it was a great way to help us connect to the characters immediately while they worked out what was happening to them and who each of them was, both before they got there and then in relation to each other once they started to understand what was happening to them. But I also felt let down a bit as character development is very important to me and that kind of slipped through the cracks. I totally support the idea of a sequel though because the film itself was the perfect opening for what could have been a great trio.... which is also just my opinion!
