My group just finished Hellfire Compact. It's a really fun book, pretty typical pacing for Paizo's AP starter books. We noticed that power level wise the book went from very easy to very hard, very quickly. My group didn't have too much trouble with the first 2/3 of the book. A couple fights toward the end had some difficulty but were fun. Not much real risk. The very end of the book was brutal though. We had a 6 man party, 2 deaths. Without specific spoilers: A keen weapon doing 2d8+30 on a crit wiped someone first turn. Also having to deal with a swashbuckler parrying and a monster with dr 10/evil for a 3rd level party was rough. They came through it with 2 deaths, not too bad for the end fight of a book really. I don't think we've ever finished the last fights of Paizo APs without a death or two.