At first glance, a look at the map, might suggest a much longer hike to include St. Sauveur, Valley Peak and Flying Mountain. Most of the hiking on St. Sauveur is in trees and although it is of comparable size to Acadia Mountain, the views are disappointing.. The other peaks are OK, but are smaller and most of what can be seen from then are visible from Acadia Mountain.
In sticking with our "uniquely Acadia" theme, my suggestion is a much shorter 2-hour hike which provide great views of lakes, the ocean and many of Mount Desert Island's peaks.
Alternatively, park at the Acadia Mountain lot and begin the trail from there. At the first major intersection (there is a signpost) take the left toward Acadia Mountain and remain on the trail until you reach the fire road. Take the right onto the fire road.
At this point, regardless of where you parked, follow the fire road SE, perhaps 1-mile. There will be a signpost that suggests to go left to Acadia, straight to Valley Cove Trail or right to St. Saveur. You take the left.
The trail begins to ascend sharply as Somes Sound begins to appear to the right. To get oriented, Somes Sound runs North-South. Directly across the Sound to the east is Norumbega Mountain. Hiking along a bit further, looking south, Somes Sound narrows and joins the ocean. The small peak just about due south is Flying Mountain. Just to the right of that is Valley Peak and to the right of that, the highest peak SSE is St. Sauveur.
As the climb continues, Beech Mountain appears to the west. Beech is easily distinguishable, because just left of the peak is a fire tower. As we continue along, Mt. Norumbega to the east becomes more prominent. As one nears the top of Ac adia Mt., first Sargent Mt. appears to the left and behind Mt. Norumbega. If you look carefully, you can make out the four-summits but they are obscured by the Mount Sargent Ridge line. The four peaks are Parkman, Gilmore, Cedar Swamp and Bald Mountain; At the top of Acadia, between Sargent and Norumbega, you can see the ridgeline of Mt. Penobscot. Just to the north and behind Mt. Sargent is Cadillac Mountain and to the left and behind Cadillac Mountain is Mt. Kebo.
On the west, Beech Mountain becomes clearer and then to right of Beech Mountain first Mt. Mansell appears and then the peak of Bernard Mountain shows up behind Mt. Mansell.
The peak of Acadia has a large cairn, but it doesn't have much of a view. Shortly after passing the peak, there is one last view to the west, which now includes a very lovely look at Beech Cliffs to the right and in front of Beech Mountain. The water is Echo Lake.
From the summit of Acadia, the trail descends into the trees and returns you to the intersection with the fire road. If you parked at the end of the fire road, make a right and you'll be back at your car. Otherwise, cross the fire road and follow the trail back to the Mount Acadia parking lot.
In a short distance, you've gotten a pretty good work out and a set of "Uniquely Acadia Views" which, short of a helicopter ride, will show you more of Acadia National Park per hour of hiking than any other hike in the park.