We are planning a full day in Acadia NP in mid-August. Reading the website it warns that, due to Covid, the Island Explorer shuttles are running shortened routes, less frequently and allowing fewer passengers on each bus. We used the shuttles in the past and found them easy and convenient. Now we are thinking we need to drive our own car if we expect to move through the park. What is your recent experience driving or using the shuttle? Any other suggestions? Are there long lines at the park entrance? Thank you in advance!

They come every 15 mins and are probably a little less crowded than they were in the past since many people seem to not want to ride on a bus with others right now. You should have no more problem with the Island Explorer than you ever did in the past.
In fact someone recently told me "parking at the visitor's center and taking the bus was so easy....it's too bad more people don't take the bus."