Most visitors to Mesa Verde only visit the Chapin Mesa area, and if your time is short, that is an appropriate plan. Wetherill Mesa is a longer drive, and there are only a few sites to visit there, so it could be skipped if you're schedule is tight. But with a half-day or more to spare, Long House and the other sites on Wetherill Mesa are definitely worth the extra driving (and the drive, like the other main park road, is absolutely spectacular and provides great views).
Wetherill Mesa is named for the family of ranchers who discovered the cliff dwellings and assisted the early archeologists who studied the sites and advocated for national park protections. The mesa is one of several north-south running fingers of land that make up the park. To get there requires winding up and down a number of these mesas, and the road there is windy and steep. Once there, you'll see that it is a much more spartan operation than the more-developed Chapin Mesa. Long House is the prime attraction, but there are some mesa-top dwellings in addition to Step House, which is a small ruin open for self exploration.
Long House is about the same size as Cliff Palace, the more well-known ruin. The tours are given less frequently and are generally smaller. There is some walking involved, about 2.25 miles round trip, but the walk is flat. Unlike the Cliff Palace tour, which is restricted to the path along the bottom of the ruin, the Long House tour allows visitors to climb up ladders and steps to visit the back of the alcove behind the buildings. Here the fresh water spring that sustained the inhabitants 700 years ago is still visible. There is also a pile of wood that is over 700 years old. The perspectives for photographs are much richer than at Cliff Palace, and it is easier to imagine what it might have felt like to live here centuries ago. Also, because this is a 2-hour tour, the ranger can go into much more detail and answer more questions.
Note: Long House is only open for tours from Memorial Day to Labor Day.