The phrase "bore heavily" can be replaced with a number of antonyms that imply interest, excitement, or engagement. Some potential antonyms might include "enthralling," "captivating," "engrossing," "mesmerizing," or "riveting." These words describe activities or situations that hold one's attention and keep them invested in the experience. Other antonyms might include "stimulating," "inspiring," "thrilling," "invigorating," or "provocative," which suggest an emotional or intellectual response to the experience. By using these antonyms in place of the phrase "bore heavily," one can convey a completely different tone and meaning in their writing, allowing them to connect more effectively with their audience.