Stargate as a television series had a number of core premises.
-Exploration. Each week they were exploring new worlds or new interactions with those new worlds. Even when they were not transporting to a new world, and stayed on Earth, they usually had to deal with something unearthly. These explorations went outside of Earthly norms.
-Likability. The audience could genuinely like the characters. Even if a main character had a personality quirk that annoyed the viewers, such as Rodney’s arrogance, they still give you more reasons to like the character than to dislike them.
-Camaraderie. There was a tight bond amongst the main characters (and even the back-up characters). That bond was shown each episode and helped to draw the audience in by essentially allowing the audience to share and be a part of that extended family. Most viewers all wished they could be with the characters.
-Fast Pace. The series were fast paced. In a way this might appear to be a general drawback as the stories started and ended in an hour. This, however, was not always the case as each series had overarching storylines that carried over for seasons at a time. However, most weekly storylines started and ended in an hour and at the end you felt as if the characters had accomplished something.
Stargate: Universe broke too many of these core premises.
-Exploration. Far too often the characters were trapped on the ship. While it could be said they were exploring the ship itself, it was exploring the same thing week after week after week and not something new unto itself.
-Likability. In an effort to do some character studies they made the majority of the characters unlikable. Even the characters we cared about and thought had some hope eventually turned out to be as selfish as everyone else. In a way this was a reverse of the previous series; the writers gave the viewers more reasons to not like the characters than to like them.
-Camaraderie. An off-shoot of the previous premise, because the characters were all so very selfish, they never formed any true bonds of friendship. Likewise we felt like we were looking in, into a morass of broken people. If suddenly the stories were revealed to be real-life and we viewers had an opportunity to go along, most would pass.
-Fast Pace. Everything seemed to move so slow. It felt like stories were drawn out to cover time. There was never a sense of accomplishment (which was a desired goal I believe) and this left the audience feeling like they were slogging along watching it all unfold so slowly.
Now, I will be the first to say that the producers and writers of Stargate: Universe purposely set out to provide for something different from what Stargate television had provided before. Some will say it worked and they enjoyed it. However, far too many other viewers were thrown off by the sudden shift of premise and this was shown by the ratings and its cancellation. Stargate fans were not given what they had come to expect and the reasons they had initially become fans were no longer being fulfilled.
The same can happen to a RPG campaign. If you are running a dark and gritty campaign, throwing slapstick into it will be too disruptive. Now, I am not saying you can not interject humor into a dark campaign, but the humor has to be more appropriate to the campaign; a darker sense of humor. Pies to the face (which you can get away with in a high-magic, lightweight fantasy setting) are not what your players want.
Determine what the premise(s) is for your campaign. Play into its strengths and then make sure what you throw in stays true to that premise. It is ok to bend the premise and throw something unexpected at the players, but it should be kept within the confines of the premise, or you risk losing your
Remember, your core premise is also the core promise you made your players at the start of the campaign.