It's worth it because it's a good game, but it's not worth it just for the different ending..
It's pretty much the exact same ending, with a slightly different voice over :/
There are technically 3 different endings, two of which are very similar. If you harvest ANY little sisters you get an evil ending, if you harvest ALL the little sisters you get the evil ending with a different voiceover.
To get the good ending you need to rescue ALL of the sisters without harvesting any.