i'll vote for planes and parachutes! and some of the features from GTA SA like custom cars, more clothes and houses/cars to buy.. hair, tattoo, girlfriends.. the weapons is fine enough although some alternatives wouldn't hurt... and what could be more fun than having a "make your character".. i mean custom your character into the style you wan't before you play the campaign
probebly much, but it can be done! with the time and money!... and i think they have both !