I'm no stranger to parks and beautiful natural places, but Acadia is like a dreamscape. There's…read morestunning ocean views from crumbling gorgeous cliff sides. There are lakes, streams, ponds, scenic lighthouses, boats, bikes, trails, gardens, crazy hikes with vertical iron rungs, rolling forest hikes, lighthouses, and more!
The main issue you'll run into is crowds.. lots of people want to come here, especially in July and August. Best thing to do, go in as early as possible, do some things, take a break, go back again after 3. If you're early, you can get a parking spot then work from there. If you are flexible on time, take advantage of the shuttles, but be warned, they may be full, and they don't run every 10-15 minutes, so plan accordingly. I would be in the park by 7, have plans maybe on a tour in Bar Harbor late morning or early afternoon, then head back after 4, and I got to all the must-do's, ie hiked the Beehive, the Bubbles, Cadillac Mountain sunrise and sunset (reserve this early as spots sell out, I booked mine 3 months in advance the minute they released and they were sold out shortly later, especially sunrise tickets), Jordan Pond and popovers, Bass Harbor Lighthouse, as well as some boat tours in the area, including very successful whale and puffin watching. For more hints and tips, I watched some YouTube videos, there's great info out there, especially the videos from Ash, a former park ranger, who has loads of helpful tips to get around and not spend your trip sitting in traffic or waiting in a parking spot.