Incase anybody is still wondering about this... I am a fan of Saint's Row. The story is fun, the amount of customization is fun, and blowing shit up is fun. Sitting next to GTA, the graphics are a step up, the aiming system is an upgrade, and I love how you can 'roll deep' with your own possee.
However, to me it feels like a shallow version of GTA. Like the above poster said, no bikes, no motorcycles, no airplanes, no boats. But it's not the lack of extra transportation that hurts it for me, there is just some feeling of atmosphere that seems to be missing when compared to San Andreas. The map is smaller and I feel like there isnt' much to discover.
With that said, if you like GTA, I think you'll enjoy Saint's Row. I do.