FSX is more like operating system for various flight simulations, rather than complete product. There are plenty of very high quality modules out there which one can buy or download for free for FSX, which include: aircrafts, sceneries, weather mods, wind and thermics simulation, camera effects, and many more.
Graphics wise FSX can vary from complete crap to almost real graphics with numerous details, depending on what mods you use, how you configured FSX, what hardware you have. The same goes for flight dynamics and damage modelling, advanced addons like the ones of A2A simulations, use external programs which calculate flight dynamics and send it back to FSX.
There are many of really amazing aircrafts made for FSX which provide real flight manuals, and require pilot to respect them. There are also plenty of super crappy addons, even payware. However you can read reviews before you buy first!
And in the end, in order to get really great FSX experience you need to spend ton of money on addons and mods, this is true.