OK, I just watched this again and it raised the same question I had the first time: why was Samara so evil? was she possessed or was it unresolved resentment against her Father for not wanting her? how did her Father know about the tape?
I'd love to answer your question but was wondering the same thing myself. Have you googled the question? sometimes you can find reviews/fan sites that focus on questions like these. I wonder if the original version is any clearer on this subject?
To find information addressing that and many other questions about 'The Ring' and the Japanese original 'Ringu' visit TheRingWorld an amazingly detailed site. The FAQ on the American movie suggests that Samara's curse came from being subjected to all the tests and incarceration at the pyschiatric hospital and could be related to her obscure origins (was she adopted as the Doctor said, or was she conceived by the Morgans? was there Chinese or Arabic spells summoned at the time of either that she carried? .... hmmmm..) Now what I want to know is in the sequel will the cursed video be available on DVD or as a download?
Not meaning to thread crap, No joke - A lady I work with and her daughter were told that they have to make a copy of their tape of "The Ring" every week and give it to someone to watch ...or else! Every Friday, she's giving away a copy of "The Ring" to someone. Always wonder...