Not ever being much of a drinker (although I have to thank the nation of Japan to at least introducing me to beer and sake) and, for that matter, a purveyor of some of the other sinful pleasures, I never really got to explore Shinjuku and its smaller sector of Kabukicho too deeply. Over the years, I have heard from some students that the place is rife with evil stuff and too dangerous to enter.
To be honest, I have walked through the streets of Kabukicho a number of times with friends after catching a movie at the Milano, and aggressive touts aside, I think Toronto has spookier areas at night.
Of course, there is Golden Gai, the famous alley in Shinjuku which has these old-fashioned bars crammed in cheek by jowl that provide plenty of libation. I never got that close to it but a couple of weeks ago, I passed by Omoide Yokocho（思いで横町...Alley of Memories）which has its own group of old-fashioned joints.
Even as a non-drinker (basically) though, there is a certain charm and attraction to East Shinjuku with all of the bright lights and big city. If my liver and other internal organs could have handled metabolic poison and nicotine, I probably would have gone into one of those joints, if only to get into the mood of some of those Mood Kayo singers.
There is one in particular that I'm thinking of now.