Okay, the good doctor wasn't such a hot choice, but I really enjoyed Wan's direction and Jigsaw's performance. The film was atmospheric and you could really put yourself in Adam's situation or any of the other victims' and think "What the hell would I do there?" Saw's got more twists and turns than an Indian Burn, and they were good twists. I think you're being a little unfair to it just because it was something different than what you were probably expecting. Saw II wasn't nearly as good IMO, but that's a discussion for another post.
As for Serpent and the Rainbow, they tried to make a semi-fictional horror film based on a nonfiction book about Haitian zombification practices, and it shows. I've seen worse films, but I wouldn't watch it again on a whim.