Combat with the Circular Saw
The Circular Saw is a bonus weapon you get for beating the game in 4 hours or less, and is arguably the most powerful weapon in the game- it does mega damage, barely needs aiming, and never runs out of ammo. It is invaluable for a Madhouse run, but handy for really any type of killing-things scenario. Here's how to get the most out of it.
While you don't need to line up the circ saw the way your would a pistol, you'll still want to use your Aim button (right mouse button by default) to bring the saw into position for an attack. This is much more effective than a wild swing, and allows you to deal continuous damage.
Go for the eyes, Boo!
Once you've got that much power in your hands, it's tempting to just ram enemies and carve into their center of mass. This will do tons of damage, but it also leaves you vulnerable to counterattack. Keeping the blade squarely in the enemy's face has the same debilitating effect as a headshot, and allows you to carve them up undisturbed by flailing limbs and tentacles. This is especially important to remember with the tall shamblers- keep the saw tilted up to maintain proper blade-to-facething contact.
The Best Defense
Because you can keep the blade going continuously, it's ideal for destroying enemies that hurl themselves at you head first. This is mainly the quadfoots, who you will learn to love for the lemming-like way they leap face-first into the saw. Easiest kill of the game. Almost as easy are the big bugs- their charges will take them straight into the blade- you just have to be a little more patient when waiting for them.