I have to say I like FS2004. Didn't like some of the previous versions, mostly because their view arrangements seemed so cumbersome and counterintuitive.
I fly just for simple fun, no complicated training for real flight or navigation ... yet. I've always vowed to do more of it, and I likely will in FS2004.
FS2004's viewing is as much fun as Aces High's, except you can't adjust the cockpit seat. Neveretheless, the virtual cockpit is much fun, and flying around from the chase position is absolutely gorgeous, especially in weather. Like being in your own movie.
Main thing is that to me, FS2004 finally feels like real flying (I am not a pilot, but been up often enough). It's fun just to hop in a plane and fly around.
The plane choices are excellent, everything from 777 to Wright Flyer, including floatplane, glider, helicopter, aerobatic, exec jet, historics, and the most popular props. Makes you appreciate the classics even more. I've always been a fan of the Piper Cub and DC-3, and particularly enjoy chugging around in them.
The weather is amazing, and the terrain realistic enough. Some day we'll probably see real satellite terrain with all the details unless terrorism and other potential hostiles keep that option too militarily useful.
Aces High is still terrific, and Aces High II should be even more fun. Nevertheless, FS2004 provides a terrific counterpart or supplement. Both are keepers.