Arrival and a doubt

The Arrival (1996) is a fast paced alien invasion movie.
It does not have presidents preaching patriotic feelgood early in the morning, no laser beams causing widespread mayhem, no tentacled monsters.
It does have conspiracy, complete with men in black (actually gray overalls), black speakers going bdddrrrrrp in an observatory, huge radio antenna arrays, a geeky astronomer not afraid to follow his instincts and a satisfying ending.

It is midway between two extremes.

What would I personally like an alien invasion movie to be like? Quiet real terror mixed with the paranoia of Philip K Dick novels, real hard-sf technology - no blinking-lights-ray-guns, and a potent dose of wonder, all splashed on a canvas of a start studded night sky. A galaxy spanning plot.

Zane Zaminski (played by Charlie Sheen) has this uncanny resemblance to Dr. Freeman of the famed game Half-Life, but the situations don't really match much.

A thought on the aliens' structure. They are humanoid, but their knees bend the other way. Like kangaroos. Like all quadrupeds. The hind legs of a kangaroo or a cheetah are extremely powerful. For running, while catching prey or while avoiding being caught as one. That's how they have evolved. Which brings me to my question. Let's forget about the scientific validity of the movie for a moment. Would any naturally evolved beings develop such hind legs and still be bipeds? and vice versa? Or am I missing something here?