I love fantasy worlds, and definitely prefer them to the sh*t-hole of a reality we've made for ourselves, but I still like my fantasy/fiction worlds to follow basic rules; things we've agreed actually exist.
Specifically, realistic laws of physics. Don't try to feed me some crap like humans being able to fly without any sort of basis to support it; they need propulsion, power, and something to keep them aloft; otherwise they come crashing right back down. Warren Worthington III (Angel) of Marvel Comics' X-Men, for example can fly. However, he wings were required to be able to support a full-sized human male; thus, his total wingspan is about 16 feet tip-to-tip. Strong enough to support him, while still keeping it realistic enough to believable.
Also, if your space aliens are going to speak to the Earth populace, don't just go with some bullsh*t about their language being coincidentally exactly the same as that of the people who encounter them. It was kinda funny when The Simpsons did it almost 20 years ago; nowadays, it's just pathetic and inexcusable.