I'm very much enjoying FSX. About the only fault I can find with the gameplay is some occasionally confusing mission instructions appearing. For example, I played one mission where I had been told to maintain 210 knots. I was then told to descend to a particular height and part way through my rather slow descent, I was told by the control tower to reduce speed to 180 knots. However, when I reached the end of the descent, it told me to level off and maintain 210 knots. It meant 180, but said 210 because it was expecting me to have completed the descent before I was told to reduce speed by the tower. Anyway, only a minor criticism...
The more significant problem is a number of random crashes on Windows 7 64 bit (I don't know if 32 bit is affected). The crashes usually happen when manipulating the menus at the top of the simulator, particularly after the simulator has been running a while. The error log reports problems with UIAutomationCore.dll. Doing some research on the web, it turns out that a number of people have this problem and that there seem to be a few problems with FSX and the new version of the system file, UIAutomationCore.dll, that comes with Windows 7. I managed to find an older version to download (from Vista) and placed it in the Flight Simulator program directory. FSX now operates using this older version and I haven't had a single crash since.
So, pretty disappointing from a Microsoft branded product, but at least it can be fixed if you're prepared to search.
(For those interested, the version of UIAutomationCore.dll that I have with my Windows 7 installation is 7.0.0.0, product version 6.1.7600.16385, file size 733KB. The old version that I downloaded is version 6.0.6001.18000, product version 6.0.6001.18000, file size 148KB. For avoidance of doubt, I would strongly advise against *replacing* the new file, even if you can bypass the system file protection. Placing the older file in the program directory is entirely adequate.)