I liked the first one in terms of confinement... the characters only had eachother, they could only work out the 'puzzle' by working together, yet both were reluctant to do so.
The second one was more clever, but that guy who reckons hes hard spoilt the whole film. I especially liked the ending... "your son is in a safe place" LOVED IT!

I dont view these films as a gorefest; its the twists and unpredictability that make them so watchable. The third should be the last one though. Its like the Die Hard films - make another, and theyll just be shite. Three is enough thanks.