Well I have played 1st and 3rd. And let me just say it was a big step-up. In the first you could not ride on motorcycles if I'm correct the guns were a bit crude compared to the third.
The character creation had changed as well. In the third your character had his own personality style and other things. In the first it was fun but my character never talked.
The graphics were also a improvement. The city the 3rd game was allot more beautiful more big, and maybe it was just me but I felt like I was in the future like 2000 years later.
But basically I don't think that Saints Row the third was a disappointment.