I don't like it when the dialogue is altered completely, but if it's only slightly, then it's not a problem. I haven't watch any series where the names are changed completely, so I can't really say about it. But, I would be annoyed anyway....
Like CC said, the difference in English and Japanese can alter the translation, but there are times when the Japanese clearly says "Stop!" but the English subtitles said "No!"
I think that could be subbed better, but it doesn't bother me as much.