Ok, so i have to weigh in on this debate between what sims are the best.
Firstly, about me, I am a real life pilot, and hold FAA and EASA commercial pilot licences (USA and European), and i am a gamer.
About the game: its not a game. its a flight simulation software. do not buy if you are looking for a
"fun game to mess around on and earn steam acheivments etc etc", nor will it teach you how to fly planes or anything of the sort. there is no arcade mode, there are no leaderboards, there are no charachter perks etc.
About the flight simulation programme: I first had my taste of flying a plane on Microsoft Flight Simulator 95 (or 98, i forget) on a crappy little PC with a keyboard and mouse. as i grew up and my interest grew and flight sims developed, i hopped from flight sim to flight sim and i have played ALOT of different ones, and in my proffesional training, i have even used things like lockheed martin's Prepar3D flight simulator with full 737 and A320 cockpit mock ups. For home simming, i dont think anything beats XP10 though. I will be drawing comparisons in my review with 1 other game which this is often compared to - FSX (Microsoft Flight Simulator X/10) (im not even going to compare against "Microsoft Flight", that sim was pathetic....)
FSX is a flight simulator, and a game in one package. it can both teach you how to fly a plane (atleast the basics) and give you fun missions to complete and rewards you with in game acheivments. It also is able to replicate, rather well, realistic flight dynamics and aircraft performance. however, i feel that FSX is a bit more buggy, alot less "modable" (free 3rd party aircraft were difficult to install in my opinion) and it feels a bit outdated.
XP10 is, i have to admit, a little less user friendly. the menus and interface do not seem as polished etc, but boy is there alot you can do. Free 3rd party aircraft are relatively easy to install, a multitude of plugins exist that you can download, such as ground vehicle tows to push your aircraft back from the stands etc and there just seems to be alot more freedom in the game.
Carrier landings for example. Xplane 10, it was very long winded, very procedural, and a bit tedious if you "just wanted to have a go at planting the damn plane on a deck". and with only the F18 to chose from, it was a bit bland. with XP10, even though the scenario would be unrealistic, i can just load a boeing 747 and click "land on a carrier" and try landing a jumbo on a nimitz carrier.
Weather is very customizable, and can download real time actual weather with a click of a button which is pretty cool.
Loads more stock aircraft to chose from
loads of different scenarios (i believe you can fly on mars if you wanted, that is atleast true of my experience on XP7,8 and 9 so i assume its on 10 too)
You can try and bring down a space shuttle from orbit, and many other things that FSX just cant do with the base programme.
Yes there are issues, yes some of the stock 3D cockpits are a bit naff and not done properly, but i have never really found it such a big deal. and if you want the true realism, be it on FSX or XP10, you wont fly stock aircraft anyway, you would go and buy 3rd party aircraft by proffesional 3rd party Devs that make accurate models and cockpits etc.
you WILL need a joystick and rudder pedals, or at the minimum, a joystick with twist function for rudders. you can play with just a mouse, but lets be honest, that sucks. FSX you can play with a keyboard, but even then, joystick set up rules.
so overall, what would i buy? both. i have both. i use them for totally different things. i use FSX and 3rd party payware aircraft and payware photo scenery to practice VFR aircraft navigation, and i use XP10 to practice aircraft procedures and general handling and flying, or to test myself in all sorts of different aircraft in different scenarious, like finding myself in a middle of thunderstorm in the middle of nowhere with various system failures.
again, i would stress, XP10 is NOT a game. it features "weapons", where FSX does not, but these are only for novelty value. they do not replicate the actual fire control systems or anything like that. This is a flight sim that enthusiasts or proffesionals can use.
If you are looking to buy your first flight sim or you want to learn how fly a plane, go and buy FSX
If you are looking for a world war 2 realistic flight sim where you can fire guns and down planes, go and get IL2 Sturmovik 1946 or Wings of Prey
If you are looking for a arcade combat flight sim, Tom Clancy's Hawx
If you are looking for a realistic combat flight sim with modern fighters, get Lock On
if you are looking for a simulator to practice advanced things on, or experiment, or design your own creations and fly them (basic engineering knowledge required or willing to take the time to research how plane maker works), then this is the sim for you.