"left button" is actually "left BUMPER", for crissakes!
Guys, maybe I am the only stupid person here, but if not, this may prove useful.
I played the game with the x360 pad from the beginning (only just bought it, so I did not experience gamepad issues from the earlier versions, so I had no experience in playing with keyboard).
In the tutorial the game says something like "press left button to see enemies out of view". I had no idea what that "left button" was (I thought left on dpad?) it did not seem to work but I blissfully ignored it and then when I played the game I was frustrated that I got constantly killed by the enemies offscreen, whom I could not see. Sometimes I had to replay a level dozen times and was able to succeed by sheer luck.
Then I watched TB's "WTF is... hotline miami" and noticed that he is scrolling the screen around like a boss. So I went back to the controls and tutorial and noticed that on keyboard controls you use shift to do it and it works like a charm.
On gamepad it is done using this infamous "left button", so I pressed every button and finally figured out that it is LEFT BUMPER (LB). I have been playing with one hand tied behind my back because of misleading naming of the button of a very crucial (yet not immediately evident) feature of the game.
I hope this helps someone other than me.