This started so strong and then became increasingly ludicrous and melodramatic

I have seen many movies that were really good almost all the way through, and then they blow it because they can't stick the landing (endings are hard). But I can't remember the last time I saw one that impressed me for a good 45 minutes at least and then just turned into a different and much schlockier movie. Oh wait, actually I can: "Sunshine". But it is pretty rare.