Abby Aldrich Rockefeller Garden - it really is amazing. If open when you are there it is definitely worth making a reservation to visit the garden.
Acadia Lobster Cruise - out of Northeast Harbor with Capt Jason. Learned a great deal about fishing for Lobsters as we went out and pulled up his traps. Then after a short cruise around the area we stopped for a delicious lobster meal cooked right on the boat. A great experience.
We did the Ocean Path - Gorham Mountain loop the first night. We took the Cadillac Cliffs option on the Gorham Mountain path which made it a little more challenging than I thought it would be - but not too bad.
Next day we did the Jordan Pond loop with a diversion up the South Bubble to Bubble Rock. We went around to go up the north side to make the hike easier and going that way it was not too bad at all. But the Bubbles Divide trail back down to Jordan Pond toward the west is not really a trail - more of a climb down from rock to rock - that part was harder than expected, but distance is not long so not really that bad.
Also did the Ship Harbor Trail near SW Harbor which was very easy. Best part of that was the area at the ocean - we were there around low tide so were able to look at some tide pools there and found an unusual jellyfish.
Went up to top of Cadillac Mountain for the sunrise which was worth the effort to get up early.
Overall a very good time on our first visit to Maine. I have to say that Acadia NP did not have the same "wow" factor as our trips to Yosemite NP and Grand Canyon NP the last two years - but those are tough to match and Mt Desert Island is certainly a beautiful place.