The moment you spot a Controller, pop those psi pills right away since their attacks start hitting you before you even realize it. When the screen gets all wavy and blurry, that's your signal to get ready because the real nasty stuff is coming in about 3 seconds. Something interesting about these guys - they'll try to spawn fake enemies around you, but focusing fire on the actual Controller is your best bet especially when they do that head-tilt thing before a big blast. Keep about 30 meters distance if you can, and watch for that distinctive blue glow around their head that means they're charging up.

Good to know that running sideways works better than backwards, and if you time it right you can actually shoot them during their attack animation when they're basically standing still. When your vision starts getting darker around the edges, that's your last chance to either pop another pill or find cover behind solid objects since line of sight matters a lot. Radiation makes their attacks way stronger so keep those antirad meds handy, and if you start seeing multiple Controllers just bail out immediately because that's usually just psychic illusions messing with your head.