On the nose, I'd give him nostril slits with some wrinkling around them to suggest development without compromising the form.
Don't add too much though, it's easy to go overboard with monster design, ideally you want to keep it down to two or three "major" design bulletpoints so it doesn't come off as tryhard and shatter immersion.
Good example of that is, again, Geiger's alien: It's vaguely phallic, vaguely human, and yet very inhuman. Those three factors came together to create the personality and design of the animalistic bloodthirsty Alien. Imagine if they'd given the alien scythe-arms, or a scorpion bobbins on their tail, or drenched it in blood, it would have been way too much and shattered that "vaguely human" bulletpoint which I'd argue made the design so uncanny! It's a bit of a hard balancing act sometimes, but it always pays to take a careful step to make sure things work without ruining the design's cohesion.
In comparison to the human dude, the monster is REALLY TALL, but crouched down to below him. You can certainly play with that a bit, making them tall and gangly is a great way to make the enemy designs imposing.