It starts out as a relaxing, joyous game, exploding baddies in a top-down combat style reminiscent of the early GTAs. It builds up to be more and more hectic, but you slowly go into the zone, so it doesn't matter. And I really do mean "joyous". You see Flamethrower has been unlocked, and you think "This game understands me", then you see the Minigun has been unlocked, and you can't help but break out a huge grin in anticipation. Once the main Quest mode is complete, tonnes of fun modes are unlocked to continue with, including a TYPING MODE! It'll take a while to get tired of this game.
The characters and dialogues are funny and unique, the level design (that fish city!), is innovative and FUN, and while it has 2005-level 3D graphics, they're used beautifully, so it doesn't look dated at all. Probably the ONLY fault I can think of in it is that some of the platforming isn't (mechanically) the best, which becomes more evident in the later, harder levels (aaaahhh....that meat circus). Even taking that into mind, I still can't recommend this game enough. PLAY IT!
I never quite understood why this game didn't get more famous. Free-roaming exploration in a living, dynamic city, combined with specific mission levels, an awesome story that developed into something you totally didn't expect, and enjoyable and fluid gameplay- It was a better GTA3...before GTA3 ever even came out. Personally, I spent most of my time talking to random civilians before arresting them and making them get down on the ground, while I'd lord about above them!