10 Things You Learn Rewatching Stargate SG-1
2. Don't Overuse A Decent Villain
Certain shows like Buffy the Vampire Slayer and Smallville would have an ever-present villain. For Buffy the villain would be a central focus of a season and appear quite often throughout it, while in Smallville the Luthor family were a part of Clark Kent's life every single day. Of course, these shows are still very enjoyable, having a villain present all the time lessens their impact when they pull off something truly evil. Or awesome (depends on your point of view).
Apophis was the main villain for the first few season of SG-1, but he was seemingly killed off in the second season, then brought back, then killed again. We got to meet the various System Lords, as well as the Replicators and later the Ori. None of these were overused as they all had just enough screen time to make us want slightly more of them.
Take Nirrti for example. We heard of her duplicity back in season 1, but didn't meet her until season 3, where she was somewhat unpopular with the other System Lords. Her stated goal was to create a genetically enhanced human to serve as a future host and we saw her attempt this about three times. While it would have been great to have her for one or two more episodes, she never outstayed her welcome as an antagonist.