I Am Legend

There's no doubt that the alternative ending is WAY better than the original one.

The first hour of this film is by far the strongest as Smith leads the audience through his day-to-day existence in an abandoned New York. It is a great set-up as the film gradually reveals both the central character's past and his intentions and there are some great tense sequences. It's a shame then that the introduction of other characters is the moment when the film become less interesting and the final hour devolves into rather generic action beats that are also let down by the decision to render the film's antagonists in CGI (which has also badly dated). It doesn't help that the alternate ending that is presented from the theatrical version is actually stronger, giving some additional context to the antagonists and filling in some plot holes. Quite a let-down when the film had started out so strongly, but it is still engaging enough.