I keep finding that films that I've been quite enjoying for the most part end terribly, and its usually that there is too much closure or an inapproipriate 'happy' or hopeful ending that doesn't sit with the rest of the film at all.
I Am Legend did this. I actually thought it was pretty good; Smith did a great job as pretty much the only character and expressed loneliness and slight madness quite well, but the ending was gash. Do Hollywood producers really have an issue with bleak endings? Do they think we need all films to end on a high note or we'll be topping ourselves left, right and centre?