Love them, the twists and turns, and trying to work out the puzzles yourself. Not seen the 5th yet.
Always have to watch the extras on the DVD's though, all about the different traps and the design of them, it's amazing the thought that goes into each trap
I don't think they are supposed to be scary like "BOO!" made you jump, but more the toe curling cringe factor as each thing happens. I guess it depends how good your imagination is and how much you get into the film, but when there is someone in a pit of needles, or having to push their face through an array of sharpened knives, or run through a room criss-crossed with razorwire I can FEEL it, and thats what gets to me with these films!