This is the artistic equivalent to having a woman ask, "Do you think this outfit makes my bum look too big?" There is NO good answer.
Your question depends on two factors: Whether your friend would welcome constructive criticism, and whether YOU are qualified to give it.
I write, and I welcome criticism. It's useful to see what you've written through somebody else's eyes. My best critic is my wife who will tell me candidly whether something is good or if it stinks. She's rarely wrong.
But a few years ago when I taught a creative writing course for seniors one lady asked if I'd take her story home (something I didn't normally do) and critique it. To be honest, it was awful, but I wouldn't have told her that. So, tactfully, I pointed out a few of the worst flaws and suggested ways to work around them. She withdraw from the class after telling the others what a [email protected] I was.
That's the situation you're in. Do you tell the truth and lose a friend, or would you friend really appreciate a sound evaluation? If you can't answer that question I'd err on the side of caution.