I want to share with you, in short, some of my experiences in playing serious themes.
Orcs were the indigenous people in a campaign I ran last winter, with four parallel groups of pioneers setting upon "a new land" (to them). The conflicts were interesting and diverse, but the orcs grew steadily less important for the campaign as we played on; the game took us in other directions. However; as part of the theme the orcs worked very well, and made for a significant part of the overall feel of the game. To have orcs as a source of anxiety, a strange element, provocative and angry (at being turned out of their own land), worked very well. The players displayed a variety of feelings towards "the green people", ranging from "kill them all" to "let them be, they are peaceful cattle-hunters". Some were involved in conflicts with the orcs, and was free to make choices on how to solve them (both violence and negotiations were chosen). It was four nice campaigns, with 33 sessions in each. Playing this kind of conflict was clearly something the players enjoyed, and found challenging. In my eyes that is good!
This summer I ran an intense "summer-campaign", with ten sessions within a week, for three parallel groups. The setting was ruled by women, suppressing the men with a hard hand. The characters were central in a peoples march to a new land, and when they came there their traditional thinking were challenged. It ended in a very beautiful way; two mighty characters got married (first time in this setting), and ruled together, and they surprised me by wording a constitution (yes, really!), were men and women were grated equal rights. Having them claiming the setting in this way, was a moment of pure beauty to me! A moment I will treasure for years to come!
To play with serious themes, and have players explore and make meaningful choices in relation to them, is a great source to exciting role-playing, great scenes, and touching characterization. It never fails to deliver moments of pure, human beauty! And sometimes brutal cruelty too!
It is something I recommend for all grown up players.