Honestly the physics isn't my worry. rFactor already had some decent projects from modders before (neil for example) and the physics engine can create great physics (game stock car). This is their "updated" engine, and looking how the tires worked in earlier progress videos I see physics being quite good. The changing weather and variation of driving line throughout a race (mainly if it rains) is easily one of the coolest new things.
They have kept pretty quiet but from the information given it has been a pretty big overhaul from rf1. The online system with mods is going to be my "make or break" situation. If they are able to produce a good central website I won't care if its just like RF1, but they said the online system is now different (one reason they charge a small fee per year) so I expect something decent out of this.
Anyways, I'm no ISI fan myself, so the last thing you will hear from me is praise.