Like everyone else, I too would like better sound and graphics. One thing that I would love to see happen though is to have the 99,000 foot ceiling removed. I like to fly expermiental aircraft to the edge of space. In FS 2004, the sky at 99,000 feet is as blue as it is at 15,000 feet. How about letting planes go higher. Maybe even blacken the sky or add some stars at extreme altitudes.
The other thing that I would like to see is more detail in major cities. For example, Microsoft did a pretty good job modeling Miami in FS 2004, but they completely left out South beach, which is arguably the most popular tourist destination in Miami. he South Beach strip looks like a minature Las Vegas, so why not include it in the sim.