Just tried it for about an hour.
First impressions; definitely much better graphics/scenery then FSX, and runs a lot smoother, I don't know what the framerate was but it's much faster then I've got in FSX with crappy scenery, I noticed no stuttering at all.
The first thing I did was go into options and set all the flight settings to maximum realism... but it still feels like arcade flying
There is definitely some kind of stall limiter, or control input modulation. I was playing in the Stearman, and can yank the stick all the way back in a slow 60° turn with no rudder and it just makes a nice smooth coordinated turn. Trying to do spins was impossible, even stalling with cross control it would just make a nice neat turn and fly out of it. (although to be fair I find FSX lacks in this area as well) It seem like it auto-trims a bit too, even though I told it not too. Basically all the controls feel waaay to smooth, like the computer is correcting all your mistakes for you, I was intentionally trying to fly bad, and everything was still smooth as butter.
So far I'd have to say I would have rather seen FS XI with the advanced scenery and framerates then this. It's very pretty and runs smooth, but it's seems more "game" and less "simulator" to me. Given my experience with the 2 free planes, I don't think I'll be paying for anything more.
I did read somewhere that the only reason Microsoft made "Flight" was that they where sick of third party developers of aircraft and scenery making more money off FSX then Microsoft was, and so they decided to create something that is completely proprietary. So I guess we'll see if they allow any third party goodies for this new game, or if all the future aircraft and geography will be MS only.