I hate hearing gripes from people about space-based movies about how it would be in real life... sorry it's called science-FICTION for a reason. If you want real life watch Nova or maybe the ISS coverage on some obscure cable channel. Here is a list of the few that bother me the most to hear complaints about. Without suspension of disbelief all sci-fi action movies would be as boring as well.... the aforementioned space station channel.
Probably the biggest. Without the growls and hisses of starship engines and thrusters, the karrangs of phaser & blaster-type weapons, and the shockwaves of big explosions you can literally feel thanks to sound systems such as THX no space movie would be worth watching. Of course sound doesn't travel through space, but how would you feel about every scene in the vacuum being completely silent, think of every epic space battle in Star Wars, every time the Enterprise enters combat with a villain of the week, the massive fleet in Starship Troopers being shot out of the sky. Now imagine them with out the ominous grumble of a star destroyer, the wisping of a tie-fighter's engines being followed by the plop of a x-wing's blasters, the creaking of metal falling apart on a battle damaged ship and the crescendo every ship in every sci-fi flick makes before making that impressive jump to light speed or warp power. Sorry, I'll keep my unrealistic sounds because in the end none of my favorites would be that great without it.
Another gripe that generally can be the difference between a movie or TV episode that looks good and one that looks cheesy are how the aliens look. Let's face it, the only practical way to get an alien to be totally un-humanoid looking is to do CGI or use puppets. No matter how expensive, CG aliens look mostly like crap. See: Non-ROTJ Jabba, Enterprise Tholians, special edition dewbacks, new trilogy Yoda (and Christopher Lee for that matter ;-) ) and those aliens that had a number for a name in voyager. Puppets, also almost always look like puppets, such as the original Yoda and that thing that laughed alot in Jabba's Palace. For me the only really good representation of a non-humanoid alien has been the original humungo puppet of Jabba. When you get down to it, it is more cost effective, which allows for a diverse universe of aliens to just throw some funny makeup and clothes on some actors and call them aliens. Both Star Wars and Star Trek have attributed this to a majority of all aliens home planets being seeded by a master race or something, but let's cut to the cheddar, cheesy makeup on some dude looks a hell of a lot better than cheesy muppets and CGI creatures.
This goes somewhat hand-in-hand with the 1st one. How much would a movie full of lazer sword fights, blaster stand-offs and space combat be slowed to a crawl if every time our heroes met a new alien they had to figure out how to communicate with them? Well.... watch a good amount of Enterprise episodes and you will find out, even their attempts to make it creative, or to add a tense to the situation generally do not work; with few exceptions. The 1st act of the episode with the Ferengi comes to mind. Other than that the idea of a universal translator in most shows is not just a tool of necessity to the characters, but also to the writers who care more about having an entertaining story than worrying about the intricacies of inter-species communication. I especially like the use of "Basic" as English is called in Star Wars as a primitive language most species throughout the galaxy at least understand. When you think about it everyone in Star Wars is an alien to us, even the humans since I don't think Earth is in a galaxy far, far away.