I live in another southern suburb (Lancaster). In my personal opinion, the Greenbriar Estates neighborhood is still nice. The homes appear to still be well maintained. Here are two links from Google StreetView that show the homes on Green Tree Lane:
1500 blk. - Green Tree Ln.
1700 blk. - Green Tree Ln.
Duncanville isn't the fast-growing city it was in the 1980s. Today, it is a mature, inner-ring suburb that is pretty much built out. Like any city, Duncanville has its nice and not so nice parts. It is also a more ethnically and socio-economically diverse community that it was back then. Recent data from the U.S. Census Bureau indicate that Duncanville's per capita income as well as the percentage of college-educated residents has declined slightly since the previous census in 2000, although they still are in line with state averages. Based on standardized test scores, Smith Elementary is rated "Exemplary" and Daniel Intermediate is "Recognized, while the secondary campuses are "Acceptable." Even though I personally believe that test scores aren't the only factor in determining a good or bad school, the fact that those campuses are maintaining high ratings is worth noting.