If you just hook a LED to mains with a resistor you get the flickering from the AC supply. To get rid of the flickering you need to remove the 60 Hz component through DC conversion one way or the other. Much higher PWM control (e.g. 20kHz) is fine too. What can be annoying with LEDs also is how much a point source they are vs incadescent bulbs, which tends to create undesired shadows. They need to be either diffused through a diffuser or a reflector, or you need multiple of them.