i have not read the book that the movie is based on, but when i first popped the disc into the player i saw that i had two versions that i could choose from. i decided to watch the theatrical release and at the end, i was confused as to why the movie had ended the way it did. it just didn’t make sense.
i read online that the movie was actually rewritten and changed from the book to end this way so that it would be more commercially palatable. so i watched the alternate ending that was on the disc and it COMPLETELY changes the entire relationship between the zombies and dr. neville. though i liked the theatrical release, the ending did feel a little forced and i felt like there were some loose ends. the alternate version really changes the tone of the entire movie and wraps up some references made in the movie earlier much better.
definitely check out the alternate ending, it is fantastic.