Please note, I played this game primarily with the "Rags 2 Riches" mod as it fixes how much of a slog the game becomes in the second half.
The game's bread and butter is shooting criminals in the face. The formula for the game is you go in an area, visit the bar, talk to some people who can get you access to a part of the map, maybe recruit someone. You go to the newly available area, murder basically everyone and loot bodies, then after doing whatever you need to do after, you go to the second part of the map, murder everyone, fight a guy with incredibly high health, then you move to the next level. Repeat. Each level has its variation on how this actually plays out but when you play you can easily see the formula. There are 7 levels, amounting to around 9 hours of gameplay, more if you play the base game. In the base game, your weapons are pathetic and are quite ineffective as the enemies have absurd amounts of health. You rely on the 1 or 2 goons you can typically get in all but 1 level of the game, and place them on corners, then you bait the enemies to the ambush point and they get smoked. Charging in all willy nilly is going to get you murdered, because the enemies have perfect accuracy and incredibly high health. In the Rags 2 Riches mod, you can still do this and on some parts its very helpful, but its much easier to just charge in gung ho with your crew and try to take on the bad guys.
Besides slowly increasing your body count with your crew, you'll be doing a few other things in the gameplay. You can Visit a shop called the "Pawn-O-Matic", despite not being automatic, is a store where you can buy armor, health, weapons, ammo, and mods that wear out over time without Rags 2 Riches. You can also talk to random people on the street, a select few will tell you stuff that can be incredibly helpful, others may do stuff for you for money, most will just tell you "Another freekin' night and no ♥♥♥♥♥." You can also visit the bar, found in all chapters but 1, where most of the helpful npc's reside, and where the recruitable goons usually are. You can also go exploring which can net you even more surplus cash to spend at the Pawn-O-Matic, ammo, armor, and health. Theres not a whole lot to be done outside of the main shooting bits of the game.
The plot sucks but its all you need. Some guy named Nikki had his shmucks beat the snot out of you in a back alley for unknown reasons, and you vow to get revenge and go around either a city or multiple cities, its not very clear, ravaging gang after gang. The Kingpin is like "yo kill this guy". Excuse me, he's more like "you ♥♥♥♥in ♥♥♥♥s better ♥♥♥♥in kill this ♥♥♥♥in ♥♥♥♥ or ill ♥♥♥♥in ♥♥♥♥ your ♥♥♥♥in ♥♥♥♥ up you ♥♥♥♥in ♥♥♥♥s." Seriously, this game has a lot of swearing, and violence. The dialogue is great, almost every line in the game has a cuss in it, and the main voice actor did a great job of making the lines memorable. Seriously, the line "♥♥♥♥ YOU ♥♥♥♥" that enemies sometimes yell when you alert them has been burned into my mind for 3 years now.
Easily the best part of the game is the atmosphere. The graphics, music, voice acting, and design of the world all are great. Forget I said music, the CD Music setting didn't work for me on the steam version, not surprised, and theres like 3 songs that loop on the radios you find in the game, albiet I do actually like one of the songs that loops. The lack of music helps create this forboding and tense and sorta creepy atmosphere. You could just be walking in this silent apartment building or run down area, and you have no idea where the enemies are hiding, while the ambient noises of cars in the background and a tin can dropping let you know that you're not alone, but you're not welcome either. The graphics don't help, which is a great thing. Almost every enemy you face is either some tattoo'd up thug looking for a fight, or some guy with a messed up face and demented smile, usually with some strange uniform to go along with it. The more regular looking people in the game are broad shoulder'd and taller than you, and the other model for the male characters is a short fat guy, it adds to the surreal feeling the game gives you.
The short version, the gameplay is a frustrating grind and eventually is hard just for the sake of being hard about 6 hours in, with Rags 2 Riches this is more or less remedied, still challenging though. Don't expect a gangster Deus Ex or anything, just a unique shooter with a nice setting. The plot is nothing special, but the atmosphere is incredible.
I say give this game definiately give this game a go with the Rags 2 Riches mod, I wouldn't say theres too much replayability in doing the whole game over again, but I would definately play the first level or 2 over and over.