its only short if you skip cut scenes and take a taxi to all the locations. a friend did that and completed it in 16 hours. i still find it good to play with all the extras such as the random character missions, races, free falling from helicopters and 50 unique stunts and 200 pigeons if you really want to get 100%.
what option did you pick at the end of the game? they are both very different endings depending what you do for dimitri, kill him or work for him.
i think i will do the missions again sometime but dont think i will do the same as a did with gta 3 and played through the whole game 4 or 5 times.