Code review is central to collaborative software development, yet feedback quality can vary widely, influencing code maintainability and developer interactions. This study investigates how large language models (LLMs) can assess code review feedback quality along two dimensions, sentiment (with a focus on harmful comments) and specificity, to support more constructive collaboration. Using over 204,000 feedback threads from 30 open-source software (OSS) repositories, we evaluate eleven LLMs, achieving F1-scores up to 0.83 for sentiment and 0.67 for specificity. Most OSS feedback is neutral or low in specificity, with highly detailed or overtly harmful comments comprising a small minority. Industry data from 45 organisations contains significantly more highly specific feedback and more minimal reviews, while harmful feedback remains rare. Deployment of our approach in commercial settings demonstrated practical value. Specificity classifications delivered immediate value, such as revealing mentorship gaps when senior developers provided more specific feedback than they received, while harmful comment classifications required careful UX framing to avoid user sensitivity. Our findings demonstrate the feasibility and practical utility of automated feedback-quality assessment in real-world environments.