its hard yes but really not too hard imo.
i started world tour on hard and i had to retry levels like 10 times sometimes (record holder is burning rangers with around 1 hour) but now i know every corner, shortcut and jump on each track.
i started the grand prix yesterday on expert and completing all 10 took a bit more than an hour on expert because i know the levels perfectly now. getting the rest of the stars shouldn´t be too hard.
its really about dedication and patience.
Thanks to Gackt for this amazing sig!