It's always impressive seeing *old* SF movies where aliens are more than a dude in a rubber suit, even if it's just an inert "dead body." SF literature has always been filled with the truly alien, but actually attempting to depict such has often been a rarity.
Humanoid form is the result of hazard and millions of random mutations. The reason why the Hollywood ETs are humanoid is economic, a guy disguised with a rubber head. Actors wish to show their faces to increase their popularity and for that reason the aliens in the TV series are almost human.
If there are intelligent creatures somewhere in the cosmos, the only sure thing about them is that they will not look like us.
ET may have any shape except that of a pretty girl:
Gestalt organisms, smart clouds, natural computers integrated by metallic particles in a magnetic field, flying plants, organic film on water, metallic skeleton creatures, giant sponges, planetary wide fungus, energy balls, solar parabolas, insects evolved in low gravity, organisms made of neutron matter, alive comets, wave vortices, thinking crystals and six meters long caterpillars may be shaped by the evolutionary pressures of another world.
They may swim in liquid methane oceans, breathe a mixture of chlorine and ammonia, be able
to see the heat, communicate by means of luminous pulses, or develop senses that we cannot understand such as telepathy, especially useful to small
Gestalt organisms such as colonies of insects with a powerful collective mind.
They could be like gigantic jellyfish floating in the toxic atmosphere of their world, or worm-like beings carrying an incomprehensible underground existence, or aquatic creatures that have evolved into an ocean-planet, with no possibility of access to fire, metals and technology but with great abstract intelligence and interesting musical culture.
They may live in space cities, away from the inconveniences of a planetary surface with earthquakes, volcanoes, hurricanes, tsunamis, and problems with local wildlife, or simply live in the interstellar space feeding on ionizing radiation.
Perhaps biological intelligence is just a transient phenomenon in evolution. A very advanced society can achieve immortality by transferring the personality and memory of its individuals to eternally self-repairable quantum devices, as time crystals or spheres of energy. In that case they would prefer to inhabit the cold outer regions of the Galaxy and even intergalactic space, away from stellar disturbances, supernovae, and gravitational waves, which could cause interference in their computer systems.
They may despise societies made up of biological organisms and avoid any contact, as we do with mites. Why would those higher entities bother to establish a communication with us? What could we tell them?