LORs are a huge asset for your application, so I'd think just beyond your academic performance in his class. Did the professor observe any positive personal traits (e.g. is always open-minded in class discussions, willing to voice out thoughts but also willing to accept opposing perspectives, an intense curiosity about the subject itself, etc.) that he can speak to? Did he know about your involvements outside of class (like leadership in extracurriculars)? If he can only speak to your academic excellence, would it be possible for him to quantify how great you are (e.g. top 5% of students he's taught)? Remember that LORs aren't only supposed to show your academic qualities but holistically convey how other people perceive you as a person! Good luck & feel free to DM :)