I have Flight Simulator 2004, and in my opinion, it is better than FSX. I only would say that under the circumstance that you visit some sites, such as avsim.com or flightsim.com and get some free add-ons for airports and/or more planes. FlyTampa makes EXTREMELY good Airport Scenery, such as the one for TNCM-Princess Julianna St. Martin Airport. That is the airport where you see the planes land right over the ocean/beach.
It has helped me take time off of my flight lessons because when I come home from a real life lesson, I turn on my computer, fly the same plane I fly in real life, go to the same airport, and I try to replicate the lesson itself. It is very realistic and it helps you get the habits you need if you want to take real life flight lessons.
The planes you can buy have something called the FMC (Flight Management Computer). This computer is very realistic, just like the one in real life commercial jets. You enter details about the plane, the amount of fuel, cruising altitude, waypoints, departures, and arrivals. All you have to do is push the LNAV button on the instrument panel, and the plane flies itself.
There is also this unique service called "VATSIM." It provides free Air Traffic Control to pilots, and it makes it as realistic as can be. You have to turn on your transponder, and you have to contact ATC before any maneuvers (Such as requesting a taxi clearance or similar things.)
My summary in a few words: Flight Simulator 2004 is only worth it if you spend money on add-ons, or, if you find cheap and good add-ons on sites such as avsim.com
