Battle of Britain 2 Wings of Victory by shockwave productions is probably the most graphically impressive flight Sim on the market bar none. If you have the computer to run it. The game itself is very deep as you run the entire war effort. But if you just want something with a great flight model and incredible graphics take a look at their website.
http://www.shockwaveproductions.com I will warn you though, you need a serious system or the load times will kill you. Especially if you download the optional multiskin pack. It adds in actual historical individual plane markings for all of the thousands of aircraft. So if you shoot down a Me 109 from a particular squadron that exact aircraft with its number is now gone. As you can imagine the computer power required for this is intimidating.
My old computer was a P4 2.4ghz, 1 meg ram, geforce 6800 and a mission load time was 3-5 minutes. There is a handy program included that shuts down all non-mandatory servies in windows that dropped the load times down to about 1-2 minutes. My new system loads in seconds though. core 2 6850 at 3mhz, 2gb ram, 8800 GTX etc....
The downside...
Coming from AH you will imediately have difficulty keeping track of enemy aircraft. BOBII is aimed at realism. There are no red tags over the plane and clouds really are for HIDING in. Take your eyes off a bogey for a split second and he is G.O.N.E.
The other thing you will immediately notice is the enemy skill levels. No AI can ever (at least not yet) really simulate a real pilot on the other stick. AH vs a top pilot is far far harder than the AI at even the highest settings. Then of course the AI wont make a truely imbecilic move by mistake as even the best players occasionally do. Even the best are human and sometimes goof. I guess I am trying to say that the AI can be somewhat predictable once you get used it whereas a real person may do anything.
I have never seen this game on the shelf at a store, I ordered it. But then I am in Fairbanks, Alaska and the nearest Real stores are 350 miles away.