Ever notice that sci-fi shows will introduce an enemy - either an individual or a race - who are pretty awesome. Obvious examples would be Star Trek's Borg and Species 8472, SG-1's Replicators and probably the Daleks...

Species 8472 and the Replicators were BOTH notable for something that made them immensely unique in terms of televisual science fiction. They weren't humanoid! Actually, neither were the Daleks but they're not relevant to this particular point. Both 8472 and Replicators were hard ass mofos, hell 8472 blew solar systems apart for kicks... and the Replicators were usually only a few episodes away from galactic domination.

Both of them were of the strong and silent variety - generally not saying anything, just being relentless in their pursuit of the enemy... beyond reason and the like. Which, naturally put them above the average bad guys... the Borg were somewhat similar but let's leave them for a minute. 8472 were no prominent in Voyager but they fell prey to the bad guy budget effect. That means that if you have a cool race of bad guys - but they're kind of expensive (as CGI effects lik 8472 and Replicator) you want to have them but not the expense. So, what do you do? HUMANISE THEM!

Even BSG did it - albeit for somewhat better founded reasons. In Stargate and Star Trek though, the reason was abundantly clear, they wanted to have their cake and eat it. What they seem to have failed to appreciate is that when the Replicators went from evil mechano to the generic SG-1 bad guys... they just lost their appeal. Species 8472 went from being all conquering and evil to being just misunderstood... Aww!

The Replicators clearly proved such a good idea that the immensely original Stargate writers decided to interject a (very slightly different) version of them into Stargate: Atlantis... guess what! They were human too and much like the human form Replicators from SG-1, they proved to be little more than t-1000 clones, albeit with the mincing bad guy Stargate cliché. There was something sinister about evil Mechano, having Five go all emo over Carter was just laughable and played more like the kind of drama you'd except from Internet social sites than anything... and to add insult to injury, they essentially became whipping boys once they got anti-Replicator guns...

Which brings us to the Borg... anyone that has seen their introduction to the Star Trek universe "Q Who" or the seminal "Best Of Both Worlds" from TNG will probably remembering thinking the Borg were immensely powerful. A juggernaut that was as unstoppable as it was relentless. In fact, writers remarked that they would have liked to use the Borg more but they found it hard to think up ways to beat them... what with them being so bad ass and all.

This changed around the time of First Contact. Presumably for reasons of scripting - it might have been hard to play against mute drones or "resistance is futile" for 90+ minutes - we had the introduction of the Borg Queen, who was essentially an arch-villain in the James Bond cat-stroking tradition that Stargate so keenly emulates/parodies. Far be it from Star Trek to let sleeping dogs lie... but we had the obligatory resurrection of the Borg Queen in Voyager.

Where she ostensibly took part in some manner of interstellar lesbian love triangle with Janeway and 7 of 9. Sounds like something out of a badly written slash fic? There can't really have been any other logical explanation for the lengths she went to in attempts to reclaim Jeri Ryan. She was one level below slavering, con attending, mace resistant, can't tell the difference between TV and real life fanboy in her devotion. Which is presumably the explanation for how the Borg went from hardcore to Voyager's whipping boy. Did people writing those episodes know about Wolf 359? An entire fleet wiped out by a single cube. Seemed like a single Voyager could wipe out a fleet of cubes (even without future tech).

It's the inherent danger, you create an enemy so powerful that you want to have them back again but the only way you can have them back is to nerf their power, which of course all but invalidates the reason for having them back in the first place. One notable exception to this nerf rule seems to be the Daleks... once upon a time, all you needed to do was run up so stairs, or to tip them over. Now they're tin pot titans that can fly, suck your face off and take a casual stroll in laser cross fire. That and they came back from being - apparently - erased from time... three times.