The vast majority of Space Operas have the same flaws. A moment's reflection and they seem obvious.
1. Lightyear is a measurement of distance, not time.
Although it could be considered colloquial hyperbole nowadays, like saying some car is lightyears ahead of another in its technology, would it still be colloquial in the same sense when there is a more basic need to space-faring humans for measuring distance in terms of lightyears?
2. Advanced technology is out of context
You can see some technologies that are lightyears ahead - see 1 above ;-) - of where we are nowadays (FTL drives), but others are barely a decade away (e.g. tv screens as part of a wall, upgraded electrical sockets, fluorescent strip lights). I'm surprised I don't see a normal 13A socket or whatever the US equivalent is for the North American series/Hollywood movies. At least the characters aren't dialling 555 in scifi movies when they need to speak to someone.
3. Historical context suits the plot, not reality
A character will introduce 20th Century music as rock'n'roll in one episode suggesting to the viewers that it's rare and largely unheard of in that century. Other characters in the same society talk about Hitler, Stalin or the politics of American Indians without explaining them to each other, suggesting to the viewer that knowledge of these historical people and their respective histories is common in that century. I find it difficult to understand a world that can remember one part but forget the other. Saying that if I think back through the histories of the 1600s, I can probably remember more about the historical events than I can the music. But the knowledge of the music isn't lost, few of us would be shocked to hear that Bach or Handel existed even if we can't name the music.
So which part of history has been forgotten or which part is taught less in the schools?
What made it even worse was that the series is set only a century away so how could they have forgotten rock'n'roll so quickly?
The saving grace for that series is that it's not alone in this using this warped concept. There are numerous other examples.
4. Time distorts
The time that it takes characters to travel from one place to another changes to suit the episode end or the length of a movie. A whole fight sequence can take 20 minutes of movie time, but only take 2 minutes of character time. It may take another set of characters two hours to get to their objective. But they arrive at the same time. How's that?
Watch the time it takes characters to travel between planets. That really does get distorted even after taking into account the time stated in the plots. This becomes worse in the scenarios where direct planet-to-planet travel isn't possible between solar systems and instead the ships have to pass at FTL speeds through gateways further out in the systems, then travel at slower-than-light speeds in the system.
Some of this could be put down to lack of continuity when reading through scripts, sometimes down to laziness but mainly I think it's so that the story fits better.
5. Non-caucasian Warrior
This is a delicate one to talk about. I guess the issue is down to stereo-typing at the casting stage and I can only applaud series like the reimagined Battlestar Galactica for bucking the trend somewhat, but unfortunately not far enough. That's a guess, it could well be that the author/scriptwriter wrote the character descriptions stating race.
There are two angles on this that bug me:
a) If the Earth is to have united under a single Government, wouldn't the race ratio for the people that were starbound be different to what we see on TV? Perhaps more Chinese, more Indian, to pick two obvious origins, than the typical western caucasian that we do see on our screens. I'd like to watch some non-Western and non-Japanese Space Operas to see if the same or reverse ratios apply.
b) Assuming we have to accommodate the lack of non-caucasian actors for some reason (why? I can guess it's down to the networks and production houses rather than the writers), then why do the non-caucasian male actors have the same roles across the different series? The male non-caucasian actor tends to be a warrior; think Lt Worf or Tyr Anasazi. To some extent even the character Ronon from Stargate: Atlantis. I admit it's not always the case, but the percentages do seem to bear it out.
6. Computer Displays
No imagination. Even the display sequence at the start of the Minority Report gives some insight into how the line between display and interface could be used in the relatively near future compared to the scale used in Space Operas. Even now, we're able to see some of that technology, witness Jeff Han's demonstration and the touch interfaces becoming more prevalent.
I can understand how displays were block graphics back in 60s tv series. The world of computers was new and the rate of advancement in the field wasn't as visible to the average member of the public (or at least to screenwriters and fx designers). However now that we've had 4 or 5 decades of living with computers, we should have a better idea of where the technologies are going. It seems wrong for a Space Opera to have more backward technology than we can find in current research papers.
I've been trying to avoid picking on any one movie or series so far, but in this case I'm going to break that rule. I have no idea why the screens flicker during the identity checks in Gattaca. Either the signal's there or it isn't. Flickering implies that the signal is only partially being received and is an analogue signal in the first place. Is the technology that bad in the future that displays flicker?
7. Childish/Idiotic Characters
Why bother? I think anything by Gene Roddenberry suffered from this, but he's not alone. Trance-Gemini in Andromeda annoyed me a lot and almost made me stop watching it. I'm glad the character was changed after the first series making for a more relaxed viewing experience.
Think of the outcry against Jar-Jar Binks. There are other examples (Dagobot) where the main cast is human and then there are one or two aliens or robots that would be more apt on childrens tv than in a serious Space Opera.
I think the scriptwriters in Farscape managed to avoid this flaw most of the time, ensuring that the alien characters were a full part of the plot with their own character development, despite having a few monomaniacal traits.
8. Infodumps/Expositions
Seems to be a major flaw in sci-fi writing in general of which very few authors, if any at all, have escaped it completely. The better authors manage to weave it into dialogue, the worst authors deftly weave it into dialogue with the agility of a wrecking ball against a concrete dam.
It is a challenge to do do properly and probably a bigger challenge for sci-fi than most. That means the writers have to step up their game. Some present a short intro, show someone reading a story, animate the pages of a book or show some history. All are forms of getting a lot of information about the world in which the series is set. I'd prefer to have a narrator (whether in type or spoken) than have bad infodumps in speech. It's why I'll always give a series a few episodes. In the first couple, the scriptwriters are trying to set the scene and just because they're no good at that, doesn't mean that the rest of the series will be bad although it does make me cringe. That does make it more awkward for feature-length films where you have to figure out how much time to spend informing the audience of the world.
So far there are a few series that I just haven't got past that stage despite there having been several seasons on release. I would've missed out on the better plots of Andromeda if I'd left after the first few episodes (those were very bad, but not because of infodumps).
9. Dirt
Why is Earth called Dirt? One Space Opera (or indeed any sci-fi tale) using the word Dirt is fine, but for other authors to use it is just plain non-originality. I'd say it's plagiarism, theft and/or copying, but it's so prevalent that would be difficult to prove. Sadly, it's become a trope. If future humans were going to forget the word, but still have enough knowledge of what the other senses of the name meant, then why isn't it called Soil, Peat, Ground or, my favourite, Humus. No, not Houmous (ah, the original planet of houmans, consisting of an oily garlic mush), but Humus.
We even have different senses for the word Earth, it can also be in an electrical context. Again, Ground could come in useful.
The use of Dirt is especially abundant in any of the series where the origin of mankind has been lost.
Beyond the multiple senses of the word Earth, isn't it more likely that the planetary government will have changed the name. How many countries now can keep a name for more than a few centuries without changing it? Add in a few annexations, formations of federations and falling empires, then there is a lot of potential for the name to change.
And what happened to Gaia?
10. Not enough thought to the culture and society
The great science fiction writers were (and are) great for a reason. When they created a world, they thought it through, specifically they thought through the implications of the technology on the society. The also thought through how society handled itself. For instance, in a cashless society, how does money-laundering occur? What are the benefits of stealing something if you can't sell it for cash?
Why?
For the side-project I'm setting up, I want to avoid a lot of the cliches and mistakes. Can't avoid them all or it may be a boring waste of time to watch, but I'd at least like to get some concepts straighter than they are in a lot of series. Some of these are tropes, some aren't (yet). I was part way through writing this and a few other articles when I came across tvtropes.org. A lot of work already exists there, all amateur (no offence) but very interesting.