Flight Simulator X is an amazing game. The graphics and realism really are great. One of my favorite games.
Graphics:
The graphics are amazing. The airplane models look real. If you are flying over the ocean a reflection of your plane will appear on the realistic water. It's a very neat effect. The airport graphics are amazing as well. There are terminals, control towers, jetways (more on this later), airport vehicles, and other traffic at the airport you choose to fly at. They all look real, and add to the amazing graphics. Oh, and if you're flying over a highway, you'll see cars driving on the road. I'll cover these more on the realism section.
Sound:
The sound here is great. When you throttle the engines up, you'll think you're in a real plane. You can hear the landing gear go up and down, you can hear flaps extending, etc. Everything you could wish to hear in a flight simulator to hear, you can hear. The sound is realistic and is different for every plane, so I doubt there will be many complaints about it. When you're in the cockpit, you can also hear warnings.
Replay Value:
This game never gets old. Why? Simply because you can never run out of things to do. There are missions, which are pretty fun that you can complete. The main thing here though is Free Flight. You choose a plane, an airport, the weather and time, and take off. Want to take off a Boeing 747 in the middle of a snowstorm? You can do that. Want to fly a Cessna 172 in perfect weather around a mountain? You can do that. You get to choose. You can create flight plans and simulate an airline flight if you want. Additionally there are failures. (Fire, engine failure, electrical failure, fuel leak, etc.) The possibilities are literally endless. There's always something new to do or try.
Customizability:
This game is highly customizable. You can download new planes online. Additionally you can download new sounds, effects, scenery, cars, repaints, and quite a few other things I'm sure.
Realism:
This is the main area I want to focus on. Flight Simulator X is amazingly realistic. Let me start by talking about the airport. At the airport you have got terminals, taxiways, runways, etc. That probably doesn't surprise you. You, however, have also got jetways that can be attached to your plane. You have a pushback truck when you're ready to leave the gate. You can call a refuel truck to come refuel your plane. You have various other airport vehicles that will be riding past while you taxi. (Additionally you can have other computer-controlled airplanes that can taxi and takeoff and land.) It really feels like you're at a real airport. Speaking of which, thousands and thousands of airports are in this game, so you can probably find any airport you want and take off from it or land at it.
Controls here can be realistic. You can set the game up to be as easy or as hard as you want it. You can choose whether you want crashes enabled. If you buy a computer flight yoke and/or rudder pedals, that will make it even more realistic. (You'll feel just like you're flying a plane!) Most everything can be controlled, adding to the realism.
The plane models are great. In the cockpit, you can choose to have a 2 dimensional panel that displays all the instruments plus you can click on any of the icons to bring up more controls (such as the throttle). Also you can fly in the "virtual cockpit" which is a 3D panel that looks like a real cockpit. (Thus the name.) You can move around it, and most virtual cockpits are fully clickable. I personally usually fly in 2D mode since I find it easiest to navigate and use. Try both out and see which one you prefer. Outside the plane looks, well, like a real plane.
In the air it looks great. The clouds are realistic. I love the reflections that appear when flying over water. While in the air if you look down you can see that the scenery looks great no matter where you're flying.
Note if you have a lower end system:
You need a pretty high end computer to run this game. If you have a lower end system, you can adjust the visual settings, but the game might not look as good, and you may not get some features such as the water reflections and jetways.
In conclusion:
Flight Simulator X is one of my favorite games. Whether you are new to Flight Simulator or not, you will love this game. If you've ever wondered what it's like to be a pilot, definitely check out this game. Just make sure you have a pretty good computer.