Mafia 2: The Revenge
You were talking to our best friend when he got shot. The whole thing was traumatizing and you just cannot let it go. You vow to take revenge on the culprit, but you do not know, who did it, so you just take out every mafia you know. The idea here is to kill every last bit of the mafia. There would be lots of enemies, but you can find some cool weapons you could use. The ammo isn't unlimited, but you can load it whenever you want in the game. The boss would be large and difficult to kill.