One example of Eve Online's emergent gameplay complexity is the economic system. MMOG economies are generally marked by hyperinflation, simplistic valuations, and little opportunity for generating wealth except killing things. By contrast Eve is a complex and balanced economy. Hunting NPCs, mining, mercenary PC killing, trading, hauling, and manufacturing are all reasonable ways to generate wealth.
There are three things of value in Eve: currency (called ISK), minerals, and ships/ship parts. Players generate wealth by mining minerals and hunting NPCs for ISK bounties. Ships are for the most part built by players out of minerals. Minerals and ships are traded on the regional markets where prices are set by the players. Demand for goods varies by day, week, and location, so there are plenty of people who make a fine living doing arbitrage.
Eve markets have a locality that makes the economics even more complex. The 66 regional markets are disconnected, so players can't easily see the prices across the entire universe. I've made a fair amount of ISK by buying stuff cheaply in one region and selling it in a more expensive region, exploiting the information inefficiency. There's also a locality effect caused by the difficulty of moving goods around. There's no mail or NPC courier service, stuff has to be moved by people. This takes time and risk, so prices tend to vary quite a bit in different areas depending on local conditions.
Eve seems less prone to inflation than most MMOGs. There are plenty of sources of wealth in Eve, but there's also a giant sink: PvP ship battles. When a ship is blown up it's value is destroyed. So even experienced characters worry about wealth. There's even a mild RTS element to the game with alliances wars over several weeks causing attrition of corporate coffers.
My war profiteering of last week was successful. The invasion of my station never happened, so I got to keep the cheaply acquired minerals. The dreaded BoB Alliance did raise a lot of hell (see this 300MB video) and have been blowing up so many ships that prices of minerals are going up all over the universe. Unfortunately now that our guests in my region are gone no one is buying my goods; I'm debating whether to hoard my minerals until market conditions improve or just haul them somewhere and sell them at a profit.