I think I may have found one of the better RTS games ever made - and it was all in German. Die Siedler III (US: The Settlers III) is a complicated, rich game where success depends on how well you can manage the various resources at your disposal.
Now, let me begin by saying you're probably better off buying the english version of the game. The learning curve isn't that steep - by the end of my first game I had a good understanding of how to succeed. The "goal" I suppose is to destroy your enemies. However, it takes a long time to raise an army. It's not like other wildly popular RTS games, where the inexplicable combination of minerals and gas fuels your war machine. It's easy to get caught up in a game like StarCraft, until you realize that you can't train any more troops because you "Need more minerals." It's only then you realize that all it took to turn a human into a steroid-crazed one man killing machine were some glowing blue crystals.
No, Die Siedler takes a more... logical approach. Soldiers are the pinnacle of technological achievement in the game, and as in real life, it takes a lot to make a soldier. Working backwards, from most to least complicated - he needs a weapon. You have to forge weapons out of iron ingots, which takes a coal-fueled fire. You can get charcoal from burning wood, or you can mine coal. You need to mine the iron ore, and then refine it into ingots.
All this mining takes miners, who (when last I checked) require food. Tasty fish come from lakes and streams, but it takes a fisherman's hut to get at them (well, I suppose it's technically the fisherman who catches the fish, but he needs somewhere to sit and write poetry in the cold winter darkness.) If you want to feed them bread - then you have some work to do. First, you need farms to grow the wheat. Then, you need windmills to grind the grain. Then, you need water and a baker to bake the bread.
Of course, you can't build any of these structures without the wood and stone that form the basis of the supply chain. And even when all the buildings are done, you need people to run them. That's what I really love about this game - when you make a loaf of bread, someone has to carry it to the mines. When you build a structure, dozens of little settlers transport wood and stone to the site.
I appreciate this game, I really do. It takes a little bit of ingenuity to win - You can't just start training soldiers because you have a barracks and a large stockpile of silicon - it takes a long, complicated sequence of interactions, and the production from basic materials of more and more complicated goods.
Unfortunately, I hear than subsequent Settlers games got "dumbed down" more and more. I guess 1998-1999 really was the pinnacle of RTS achievement. For a more in-depth discussion of that issue, head over to Snook's post on an upcoming space RTS.