It is easy for more foolhardy individuals to think of humans as vermin given several of their more undesireable traits and various deficiencies, but they most certainly are not! When being resourceful and determined - which they usually are if "Independence Day" is anything to go by - they can be a formidable threat. Just not individually of course. This native of planet Earth reproduces at a very modest trot, and have reasonable numbers as a result. Their intelligence is quite fair as well, with certain sub-cultures being particularly eccentric and creative. I'm obviously talking about those most queer specimens from Japan.
Of course, if their minds are not properly cultured, it will fail them. Meanwhile, their physical traits are not spectacular - as I had hinted at earlier - but this alone does not make them a nuisance. Quite the contrary. Though they are easy to overpower, easy to injure, and easy to beat in a race, I believe they are the sum of their parts more than anything else. These parts may be mediocre individually, but all told, what they have is flexibility. Humans can be almost anything, ranging from clever scientists, to skilled artesians to stubborn fodder that just won't go away. Further exemplafying this, is what happens when their virtues are all stellar. The humans will inevitably create a very troublesome Übermensch that will require getting thrown into a molten vat of metal to destroy. Even then, it's in their character and their creations' character to defiantly go down with a thumb sticking up and out.
If anything though, humans are beasts of infinite possibility.
Appearance
I admit, I can't shower much praise for them here.
For starters, they're not very much to look at, being more or less bipedal apes that are largely hairless save for the bit on top of their head and a few other small, minor places. Naturally, these apes don't have any sort of scales, shell, tough hide or any other form of natural protection, and are very visibly soft, with vulnerable skin. This skin can range from being very pale to tan, to a type of brown, and also to a very-very dark brown that's almost black but not quite due to the melanin in them. Naturally, the humans are lazy, and just call these darker variants of themselves 'black' and ignore the subtleties. It's such a massive issue culturally, that I'm certain a few of them reading this had to go over that line more than once to make sure they understood it correctly. Anyways, being a type of ape, they have two arms and two legs, with just one opposable thumb on each hand. There's five fingers on a hand, and five toes as well, but there are no claws or anything of that sort, though humans do find that their nails come in handy for picking at things.
I note that their heads are very peculiar in how lacking it is in regards to defining features. They do not have a snout that houses an extended olfactory area, nor do they have any substantial jaws that can snap and bite. Their eyes are not even very powerful, and their ears simply have these flaps of cartilage to try and funnel in sounds. Even so, they still have a small, practically vestigial nose, a pair of eyes, and a single mouth with rather dull, omnivorous teeth. I like to think it's representative of how they can't make up their minds on even what to eat, but that's another topic for later. Perhaps thanks to their facial plainness, their features are quite mobile out of necessity, and contort into all sorts of different patterns to express their emotions.
The mammary glands of human females are also worth mentioning, especially since they play a very large role in human culture as well. They only have two of them on their chests, these saggy things with darker colored feed-ports called nipples, and due to their growth being affected by their hormone levels, humans appear to be obsessed with larger ones as they indicate fertility. Fortunately, this obsession hasn't spiraled out of control beyond a few rare exceptions, and they generally have a specific range they prefer, though this does vary from sub-culture to sub-culture. I note that the larger ones are very soft and warm, and make for a pleasant head-rest, so I do understand their madness, just a little. Unfortunately, the male reproductive organs do not have such utility, though I do note that humans have invented not one, but several different types of penis soups and stews, which may or may not be worth investigating. It's typically a flaccid thing that is covered with slightly darker skin and dangles between their legs, but it will grow longer and stiffer with proper stimulation. This hardening is deceptive however, as there appears to be numerous cases of penile fracture as it would seem. Like with female breasts, humans also obsess with the size of the male penis, believing size equals potency and, apparently, ability to perform.
Their obsession about their own reproductive organs and bodily dimorphism is as baffling and as it is infectious. Still, I digress. They are a species evolved for function first and are very utilitarian and bare, and their appearance makes this very clear. Everything we see of them is mediocre, but that is very misleading as the humans are more than meets the eye.
Anatomy and Physiology
Looking at their parts individually, it is very easy to make the foolish mistake of thinking that they are nothing more than a nuisance to be slapped aside. However, such individuals forget their ingenuity, though this isn't about their ships or power armors. This is about what is inside that tenaciously sturdy can of a power armor that refuses to open, and that you need to get someone to help open.
Human life spans are not the shortest, but are still on the shorter side, living to be roughly a hundred years or so. This is partially offset by a reproductive system that is constantly on standby, though the gestation time is nine months and it will take roughly a decade and a half to produce a combatant. When dealing with the native flora and fauna of Earth, this is actually quite excellent, as their offspring are of very high quality mentally. This is where they shine. Their brain activity is very lively and adroit out of necessity, and requires a high caloric intake to maintain. For this reason, the rest of the human body is lackluster. Where other species will make technological progress very slowly, the human brain will allow them to progress at a much faster pace once they get into stride. In comparison, species such as the Aos Si are so long lived that they easily become detached and aloof, ceasing innovation once when they are comfortable, while ones such as the Oruk will primarily only use what is on hand and use it well rather than make something better due to their very primal focus. Both are physically superior to humans. Meanwhile, said humans have a body that is only good enough to just survive, and a life short enough to remain uncomfortable yet long enough that they will become experienced enough to put it to good use.
Assuming said mind is cultured properly and that they bother to use the blasted things. I'm certain readers will be able to tell that I am most miffed that comfort prevents them all from such.
I've put much focus on their brain since the rest of the body is neglected in its favor. Regarding the rest of their body, I note that they only feature a pair of eyes, a single heart with four chambers, a pair of lungs, a pair of kidneys, a single liver, a single stomach, a pair of testes for males and a pair of ovaries for females. I could go on, but the performance of these internal organs are not noteworthy, as they are the sum of their parts more than anything else. The one thing besides their minds that I will say that is remarkable though, is their taste. Human flesh is utterly delectable, but it is their organs that are truly special. The warm, slippery coils of their intestines are chewy, yet full of flavor and make for the most wonderful of sausages, while their eyes are a special goo filled treat, especially when served in a wine sauce. Their hands and feet are full of fatty collagen and fall apart in the mouth when properly stewed in a flavorful jus. Meanwhile, their tongues and hearts are meaty yet pleasantly firm and chewy all at once. I am particularly fond of their kidneys and lungs when used in haggis, though I advise caution as some of them smoke, while others have stones.
And of course, the liver and brain cannot be forgotten.