I like them most of the time, but it depends on how well they're written (obviously), how major a character they are and sometimes which fandom. I'm fine with making OCs for small characters, filling in a gap, or making an OC child for your favourite pairing when they don't have any canonically. I'll only like an OC love interest in a limited number of fandoms where the canon character has no long term canon partner.

Sometimes they fit and sometimes they can seem out of place depending on what the fic is and tbh, they're hard to write. I'm lousy at it so I applaud anyone who can.