I'd say there's no shortage of demonstrations of complexity emerging from the iteration of simple rules -- fractals like the Mandelbrot set, simple edge-matching rules for aperiodic tilings, the logistic map, etc., etc.

What makes Conway's Life particularly "catchy" (along with other 2D CAs) seems to be the motion. Humans love watching stuff move, especially when the motion is partly predictable and partly surprising -- i.e., like a screen-saver, not like TV static. And they like watching things blow up. A lot of Lifenthusiasts probably got their start by aiming gliders at carefully balanced Life patterns and gleefully watching the resulting explosions... it's a lot more fun than actually blowing things up, because you can always hit Undo and run it all over again, no harm done!