I had high expectations for the film, and was let down. I don't think it is nearly as good as 28 Days Later. I think the acting was fine, and I didn't mind the scenes trying to set up sympathy for the characters. Maybe there were too many of them, as I had a hard time maintaining an interest in them all. And in the dark of the cave, it was hard to tell them apart sometimes.
I agree that every jump was signposted, but I still jumped (and, embarrassingly, screamed like a little girl) almost every time. So because I went to a film knowing that part of the entertainment of it is to make me jump, I'd say it did pull that off, and in a much more interesting film (story, acting, location) than other horror films. However, not only were the jumps signposted, so was most of the story. Ten minutes into the film, my friends and I huddled and we all knew that Juno had been sleeping with Sarah's husband, and that they would be the last two left in the cave, and that Sarah would be the only one to live, and even that Holly would be the first one to go). Maybe that is part of the fun of horror films, to guess who goes first and who makes it. But it wouldn't be bad to be wrong, to be surprised by the story as well as the choreographed jumps.
I was very annoyed at the attack scenes. The camera work was so violent and thrashing that I could never tell which character was thrashing at which. Was the woman kicking the creature? Whose neck did that thing just bite? What is going on? Only thing to do is to wait for it to end and count the dead.
The audience I saw it with was fun. When we first see the creatures, one said in a Gollum-imitation voice, "Smeagol." When Sarah finds Beth still alive, and per Beth's request whacks her with a rock to put her out of misery, someone said, "I'm not dead yet." And, of course, people were turning around to look at who it was that kept screaming like a little girl, laughing and pointing. I took revenge on my friends, however, but picking up the bag of popcorn just before one scare scene, knowing that my jump would throw popcorn all over them. It worked.