Hey Kenny,
P3D does not have active weather like FSX. They couldnt negotiate that in the purchase.
P3D also does not have a boot screen. You boot up into a flight. There is a addon that you can download that will allow you to choose a flight and load straight into that.
The planes that are in FSX are not all in P3D. The Maule, Mooney Bravo, and Piper Cub are, as well as some classics from JustFlight.
Some people have reported slower frame rates with their rigs, while others reported faster frame rates. I am one of the people that have massively faster frame rates and pure, good performance, though still in the 20's. Some graphics cards are not handling the new Shader system well.
You should see some improvements to the ground terrain textures. To me, they seem much improved over FSX. I do not get the stutters anymore, no pink runways, things disappearing, etc. Pretty stable, unless I am in a really loaded up plane and in scenery like ORBX with alot of things active. Then its downhill from there.