I vaguely recall an article describing reasons why really exotic (e.g. galaxy scale) life doesn't make a whole lot of sense. One problem is that no matter how it is organized or what it is made of, light speed prevents it from communicating rapidly. If it doesn't communicate rapidly within itself, it can't develop or evolve much in the lifespan of the universe, at least so far. You can deduce various constraints on "intelligent life" without making simplistic assumptions a priori that humans are normal, but rather starting with what we know about physics.