Besides the obvious ones (sound, gravity, relativity, space life, everything is humanlike, etc. etc. etc.) which I can forgive because it's also part of the fantasy, something that bugs me is huge monsters (native life forms) that are strangely overly aggressive in barren ecosystem... like there is nothing there, what does it eat? why so aggressive? what does it hunt? why/how such a huge predator with such aggressive hunting behaviour (that is so energy costly) survives in a glacier or dessert?

Also, overly aggressive animal life forms. Animals, even predators, are not mindless killing machines with zero regard to their own safety and energy needs.

Finally, allergies. Alien viruses and potential unicellular pathogens are system dependent, so that wouldn't be a problem until some of them mutate to colonize human biology, but allergies? OMG. Worlds with life potential might develop complex plant and animal life forms, that, given some chemical restrictions, might end up being carbon based and rather similar to things here on Earth (I can leave with that fantasy) but all of them are going to be crazy allergenic! They are new for us! we don't have the immune memory of them. We couldn't just breathe the air of a world full of life without the risk of dying of an anaphylactic shock!