Miyajima is a popular tourist destination and has a ton of shops and restaurants open during the day. By night however, the whole place seems to become a ghost town. We stayed at a Japanese-style (with futons and tatami, as opposed to western-style with beds) lodge on the island.
When the tide is out, you can walk to the Torii gate in front of Itsukushima Shrine. When the tide is in, the gate seems to float and is quite picturesque.
The wildlife of Miyajima is also something to behold. There's monkeys living on Mount Misen and the ever-elusive raccoon dogs (tanuki) scurrying about after dark freaked us out the first time we saw one...not really know what it was. The deer on the island are considered sacred, but they don't seem too high and mighty about it. They'll still try to eat your guidebook.