When somebody thinks you are a famous or at least an important author, and they ask your to read their beginner's work - and place an opinion on it - don't. Don't do that. They don't want to hear your opinion, they want to hear praise. Even if you praise it for an hour, as soon as you hit 'but', it's over. Fan becomes enemy. Young writer becomes an angry old writer. There is just no way out of it, that would benefit anybody. Young writers and the truth are two forces at war. Don't get in between. 

If you really, really, really must get into that, just highlight the good stuff about the piece. Say it has an amazing narrative, characters are well developed, the style is young and fresh and perky. Whatever. Just lie. In this case a lie is a much, much better alternative. BELIEVE ME. I've been there. Both sides.