What kind of story are you expecting?
I never played the first Saints Row, but I was able to easily follow the story of SR2. It is typical gangster storyline, you are trying to rebuild the saints into a powerhouse in Stillwater. Need to take out the three rival gangs. Besides the disappointing ending, I actually enjoyed the story in SR2. Certain things happen during each gang storyline which lead to motivation for not only your gang, but rival gangs. Ways of taking out enemies is pretty brutal and visceral at times too.
You could always rent it first. I spent about 13 hours doing activities before hitting the main storyline and finished it in 10 hours. Of course I did play it on the easiest difficulty to plow through the story so I could get back to doing more activities. The side mission activities are pretty damn fun, and give you character bonuses (unlimted ammo, unlmited sprint, etc) which help out your character in the storyline missions.
I'm probably going to send this back tommorrow, but will pick it up for 30 bucks so I can mess around in the game some more.