I used a bunch of third party freeware to make the last Flight Simulator (Century of Flight was it?) look more realistic: better looking water, clouds, moving and static ground traffic at various airports, more and better looking trees in certain areas, more aircraft around airports (on the ground and air-traffic), fireworks (depending upon your date) in certain areas, cars and other traffic in certain areas, more boats (sailboats to big ships)... the list goes on. Lots of dynamic scenery can be added. Really makes Flight Sim look fantastic as I preferred to fly smaller and slower low-altitude aircraft like Ultralights for it when I wasn't tooling around trying to fly formation B-52s alongside Millenium Falcons and the Firefox jet (from the movie of the same name) in multiplayer. There's a ton of free add-ons for flight sim... look around. You'd be surprised how nice you can really make it look. Check out
http://www.surclaro.com for some stuff (but there are a LOT of other sites out there too).
That being said, I'm anxious to hear/read more about the new Flight Sim.