The weather/scenery is fantastic - almost too realistic, since (as in real life) you can't see the ground most of the time!
Same with the GPS (being able to see the terrain) and the Air Traffic Control.
My only grouse is that the actual aircraft don't seem to fly as well. Bring a 737 in on ILS, 'by the book', turn off the auto-pilot and auto-throttle at 1 mile and the nose goes way high, you have to wind on trim in a hurry. Even then, you have to land nose-high unless you use 40 degrees of flap - which is NOT right. That never happened with FS2002, smooth transition.
My other problem is that I love prop twins - but the Beechcraft Baron is a 'dog'. Needs full boost to do anything, climbs like an arthritic pensioner, you simply cannot trim it level on a landing approach, the nose keeps pitching up or down whatever speed you hold. And no better aeroplanes available to download yet - not from sites I trust, anyway.
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci