The Museum of the Southwest is primarily an art museum. It hosts traveling exhibits and permanent exhibits. There is also a planetarium and the Fredda Turner Durham Childrens' Museum which is a very cool kid friendly museum housed in a separate building on the grounds. During summer there are free Sunday afternoon lawn concerts on the museum grounds featuring a variety of local and regional musicians. These can be tremendous fun for all ages. Christmas at the Mansion each December features lavish Christmas decorations and a gingerbread house competition. Some of the gingerbread houses can be amazingly large and complex.
Septemberfest is the museum's primary fundraising event of the year. It hosts dozens of artists from around the world. Other features include live music and a wide array of food booths on the museum grounds. I would not make a special trip to Midland to see the museum, but you would be remiss not to visit if you are already in town.