I really don't know what to expect with the rally in GT5. If it was just going to be included like in previous games then I would assume it would be quite similar but now the official WRC license is involved it changes things a bit.
I am hoping for some real car damage, bumpy changing surface courses, ideally point to point. With normal GT5 races there is 8 to 16 cars on the track but with a point to point rally there is only one car to worry about so I am hoping some of the extra PS3 power can be put into adding finer details like tyre trails in mud, better dust, debris flying up and muddy/dirty cars.