I've only done the Sunday and Clubman events so far as my girlfriend had been around all day, and only used the DS3 pad so far.
As there's no option to change the controller sensitivity (as far as I could find), this demo seems extremely twitchy to me, even the R2 and L2 buttons for accel/decel seem overly sensitive, perhaps that's just me.
The frame rate is also terrible for me, it's very inconsistent and therefore off putting. The graphics do look nicer however.
My overall feeling is that there just seems to be too much grip, I've purposely been trying to over drive the car and never lost control, just a bit of a drift in the 350Z. The replay I watched didn't look realistic at all during these moments, especially for something on sports hard tyres, but the suspension movement has definitely been improved.
Perhaps my favourite thing about the demo over GT5 is not the sound (it's the same), graphics or physics, but the presentation of the menus and loading screens, and the improved loading times. I'll try the game further before making any final judgements (and I understand this is only a demo), but so far I feel that overall GT5's physics are better, how much of this is related to the steering/button sensitivity I don't know.