I'm so glad I played SR3 before 2. I really enjoyed my first playthrough of 3, but then I played SR2 and it was just so much better; funny but not retarded, great gameplay and a proper gang feel (Eazy G)... Saints Row 3 was shit in comparison.
As for 4... They seem to be taking it to a new level of "LETS MAKE DILDOES AND RAPABLE CHILDREN INGAME THAT WILL BE SO FUNNY XD XD XD" as a substitute for actual plot and storyline