It's really suspensful from the very beginning, the cast and performances are terrific but sometimes the pacing feels a little "off" - but in general it's a good film.
BUT, what really spoiled it for me is the post-release marketing. The whole thing in the TV ads about how "it's the most shocking ending in years" REALLY spoils the entire movie. Because of that, you sorta guess where this is all going within the first 5 minutes and just sit through the ride (albeit in a stressful and entertaining manner) until it finally unfolds.
It remains a very good film but I would have much preferred figuring out the "shocking ending" on my own.