The summit of Haleakala is bit like being on Mars - barren, reddish in color, and cold. But it isn't lonely as Haleakala is one of the most popular attractions on the island of Maui. Each day many vacationers travel up the winding road to the summit at 10,023 feet to watch the sunrise atop the dormant volcano. Most do so in rental cars, but a some choose a company offering a bicycle tour downhill. You will want to watch out for these groups of riders moving much slower on the road.
The scenery is awesome along the way and at the top. From the top, if you look to the south you will likely see the peaks of Mauna Kea and Mauna Loa on the Big Island. During the middle of the day a cloud layer often forms over Hawaii between sea level and the summit. So if it looks cloudy before as you start to make your way up the mountain, keep in mind it is likely clear and sunny on top.
One does not really need to hike in the upper wilderness area to see great views. There are several lookouts along the road and views from the visitor center. You can see nearly all of the trails from these lookouts at the summit. Just because Maui is a tropical island, do not be unprepared when heading up to the Haleakala summit, as it is often freezing up there. You will need warm clothes and sunscreen if you plan to embark on one of the trails.
A great place to explore is the lower park of Haleakala National Park and the Seven Pools area. But you need severals hours and be willing to take the Road to Hana and then some to reach it.