I've never seen 1 or 2 but I don't think I need to. This is a nice self-contained tale of an old man who brings vigilante justice to a seedy part of town. Having been given the OK by an angry cop to do what was required he's basically given carte blanche to kill people left right and centre, and that is what makes it so enjoyable.
It's funny that the neighbours seem to take great delight in bad guys being taken out by traps and in some cases being killed right in front of them.
It's seriously silly. Loved it.