I didn't watch the movies
Kill and eat people, acid for blood. A weird little tongue thing with a mouth on it they use to kill people. They've got all sorts of potential for gribbly ways to kill survivors lol
They are fast, stealthy killers with impressive intelligence and built as a perfect killing maching. They have acidic blood, which is both a defence and also known by the xenomorphs to be corrosove enough to use as a tool.
Another interesting thing is their ability to adapt to the environment, especially the biology of the victim they're birthed from. They often share characteristics, as illistrated in "Alien 3", where the xenomorph was birthed from a dog and their appearance resembled a dog.
Finally, they have a Queen and also a potential "hivemind", which not only works on the xenomorphs into creating an efficient army (like ants), but also (and perhaps more terrifying) can induce nightmares, visions and even a form of religious fever in potential hosts, making them even willingly give themselves to the xenomorphs.
The face-hugger stage is perhaps the least worrying aspect about them.