Honestly I'd put the giant gap between SR3 and SR1. SR1 was basically a GTA clone to me. Didn't really split off into its own awesome identity until SR2 (and stayed there reasonably in SR3).
I haven't played the other Saints Rows like you guys but if SR2 is anything to go by then SR3 is going to be incredibly fun. I hear SR3 has a shark gun?
Also has a giant, floppy dildo for a melee weapon. SR3's problem is that it tries just a bit too much and goes so overboard all the time that the wackiness loses it's impact (it also has worse pacing and other things). It's still good, but it doesn't hold a candle to SR2, imo.