The first Saints Row had a feeling to it. The feeling was of a group of guys (Volition, the game's creators) who, after finishing GTA San Andreas and loving it, wanted to keep on playing. So rather than simply play the game over, they made their own.
Saints Row 2 has a feeling. It feels as though the guys behind the first game sat down and said to themselves, let's make the sequel BETTER. Uppercase letters being deliberate. Whether they knew, or at least suspected, that GTA IV would be so much better graphically that the previous GTA games, but would trade its new, polished looks for a sharp decline in the quality of the gameplay (and in the overall FUN of the game) is anybody's guess.
But what Volition did do with SR2 is make sure that the FUN came first (and again was presented in Uppercase). Something they also apparently did was to sit down and read through the "things guaranteed to seriously piss off opponents of violence in video games" handbook. SR2 is violent, but violent in a ludicrous, over the top completely cartoon fashion. Which only adds to the fun.
The story missions are fairly standard fare, being based around the traditional drive to a place/kill a guy/sit in a vehicle and man the guns format, but they are all handled well enough. Where the game comes into its own however, is the diversions and side missions. Volition seem to have decided that if you do something, it should be recognised and (often) rewarded. Jump onto the front of a car and when the vehicle starts to move, you suddenly find yourself "vehicle surfing". A Tony Hawk-like balance meter appears, stay balanced on the car for long enough as it chugs along and you get a reward. There are many more little hidden gems like this, just for fun.
The city of Stilwater has been expanded since the first game (and an explanation for this usefully provided as part of the game's storyline). Volition also add to the mythology of their universe by self-referencing. Several of the characters from the first game reappear, some have changed, some have moved on.
All in all, this is a game that I can't recommend enough to any fan of the "sandbox/open world" style of game, to anyone who enjoys the GTA format, or to anyone who simply enjoys games which don't take themselves that seriously, while taking the task of entertaining the player, very seriously indeed.