The Loop Road, which is part of Acadia National Park is great but only half of it is ocean view, the rest is light forest and ponds. For more ocean views, including fishing harbors, go to Northeast Harbor and Southwest Harbor, which are small towns on Mt Desert Island and not within the National Park Boundaries.

The road from Northeast Harbor to Southwest Harbor goes around Somes Sound, the only fiord on the east coast. In Somesville at the top of it is a beautiful little bridge reflecting in a lilly pond.

The view from Cadillac Mountain is worth the detour

Thunder Hole is best about one to two hours before high tide. But when it’s relatively calm, even then there is no thunder and it doesn’t look anything like the post cards (or your memory of it from 20 years ago)

The shuttle buses do seem to go all over the island, but there don't seem to be that many of them. I think you'd probably have a pretty long wait if you were depending on them to get around. Traffic was not bad and there was parking in all the lots and plenty along the side of the road.

Jordan Pond House really is wonderful. Popovers on the lawn overlooking the Pond is a great way to relax. If you don’t have the kind of pans they use, buy them at the gift shop. You can really make popovers just as good (and you do not need their popover mix) as long as you have the correct pan. It’s $17 there and $16.95 on Amazon so you might as well get it there. The wait for a table around 4-5 pm is only a few minutes; at lunch and dinner time it’s much longer.

If you go to Bass Head Lighthouse (near Southeast Harbor) the best view of the light is from the path to the LEFT of the parking lot.

The town of Bar Harbor is completely touristy (I think about 3 of the hundred or so shops did not sell Tee shirts, the rest did) but it’s cute and worth walking around in.
Lobster Rolls at all the restaurants in Bar Harbor are about $15. The road coming in from Ellsworth has many lobster pounds/shacks and the prices are about half that in Bar Harbor itself.

The paved 'Shore Path' from the town pier around the harbor (back side of town) is nice.

We were on Mt Desert Island for a total of 27 hours (from about 1pm on a Wednesday to 4 pm on Thursday) during which time we: had lunch and walked around Bar Harbor, drove the Loop Road twice, had 'tea' at Jordon Pond one day and lunch there the next, stopped at Thunder Hole two times, drove to Northeast Harbor - around Somes Sound to Southwest Harbor and Bass Head Light, had dinner at the Thirsty Whale and did a lot of shopping in Bar Harbor. So basically that amount of time is sufficient to really see most of what there is to see on Mt Desert Island. If you want to hike or bike then you need more time - we only did short walks, no real hikes.

Acadia is wonderful. But the views, the food, the ambiance – are really just about as good in Camden/Rockport and further south so if you are coming from the south think about if you really need to spend those extra hours driving.