Damn me and my morbid curiosity, I want to know what fic you're talking about! haha

I'd say no? Unless the author seems like the type to want to make a career out of writing, I'd say just stick to what you like. And unless is just... glaringly bad grammar or punctuation, etc, I wouldn't go too deep with the crit. Maybe it's a person just starting out, or someone whose native language isn't English, etc.