Creative Differences: You bet. Tracy Tormé reportedly fought tooth and nail for much of the first two seasons. He ultimately left partway into Season 3 because of both this trope and to take care of his ailing father. He was interested in returning for Season 4, but cited this trope in regards to working with David Peckinpah (a holdover from Season 3).
John Rhys-Davies was noted for always complaining during his time with the show. This always rankled the writing staff, but it got ugly during Season 3 when a new writing staff came in. This ultimately led to Rhys-Davies being fired over his criticism. Cleavant Derricks recalled the firing of his cast-mate in an interview, implying the creative differences also led to the very unprofessional announcement of his firing. (Rhys-Davies had been fired casually in public in front of the rest of the cast and crew.)
Creator Backlash: Tracy Tormé was vocal in his criticism of the way things were going before he finally left, but all of that was nothing compared to when he saw the "Exodus" two-parter. Quote found on Earth Prime:
"I will unabashedly tell you I thought it was one of the worst pieces of television ever produced, and the low point of the entire series. If you look at it, there are signs of the lack of caring, lack of thinking; lack of everything. There are giant logic holes, scenes that don’t edit together well, poor production values, poor performances, poor writing; it was an absolute utter embarrassment. It goes way beyond either of the shows I took my name off on Star Trek."
Directed by Cast Member: Jerry O'Connell helmed five episodes - "Stoker," "Slidecage," "Lipschitz Live!," "Data World" and "Roads Taken."
Executive Meddling: The main reason why the show lost its politically- and philosophically-charged plotlines, in favor of "Movie Rip-Off of the Week."
In a fun subversion, though, Tormé was once able to pull this trope off to his advantage. His bosses were completely opposed to "Invasion," but Tormé so wanted to do it that he went over their heads to their boss (John Matoian). Matoian liked the story, so he overruled the people that had been overruling Tormé. Oh, and unsurprisingly, "Invasion" became an instant fan-favorite.
Friday Night Death Slot: The series stuck it out for its second and third seasons on FOX's Friday night schedule. Most of Season 4 aired Monday nights on Sci-Fi, though the last six episodes premiered on Fridays to air along with Farscape and First Wave as part of a new channel line-up. Ratings were actually good despite this move and stayed that way throughout the fifth season.
The corrupt Lt. Graves in "Time Again and World" sounds a lot like OptimalPrimal.
McLeaned: Arturo is the most cited example, though his actor was fired instead of just leaving the show. Wade and Quinn avert this because their characters were alive (though only technically in the latter case) after their actors left. Possibly Colin, but it's hard to say because the series never firmly stated if he was still alive or not.
Old Shame: Writer Paul Jackson has very little positive to say about his last episode, "Slither."
The Other Darrin: Quinn's mother was played by a different actress in Season 2 due to Linda Henning moving to Los Angeles. When the series moved production to LA, though, the original actress was called back up.
Quinn's father was played by three different guest actors over the first four seasons.
Brain-tissue-harvesting Evil Brit Col. Rickman was played by Roger Daltrey in his first appearance, "The Exodus" two-parter. Daltrey was reportedly unavailable to continue on for the rest of the season, so Neil Dickson was cast for remaining appearances. The change was explained a la The Nth Doctor.
In the same episode, Tracy Tormé's wife appears as a bridesmaid.
Any time Rembrandt met one of his doubles, they didn't have to resort to fancy camera tricks, as one or the other Rembrandt would be played by Cleavant Derricks' twin brother Clinton.
Recursive Adaptation: Plots and elements of the comic book series eventually found their way onto the TV series, though it's hard to say how much of this was on purpose or just a coincidence. Narcotia to Season 4's "Just Say Yes" is considered a given though, as the former was written by Jerry O'Connell (who was a producer in Season 4).
Recycled Script: The movie ripoffs in Season 3 are the most cited examples among fans.
Series Hiatus: Following the Pilot's completion, FOX ordered a full season. However, the network proved unsatisfied with the initial episodes and ordered a hiatus after "Luck of the Draw" for a Re Tool. FOX always intended to bring Sliders back to finish out the order, but there was no room on the Fall schedule—leading to almost a year-long wait in-between Seasons 1 and 2.
Teasing Creator: For years, Tormé remained purposefully vague over which Arturo slid in "Post Traumatic Slide Syndrome." It was only until about 2010 when he finally laid it out.
Seasons 1 and 2: Several episodes were broadcast Out of Order, and at the end of both seasons the show was cancelled before being brought back by fan petitions.
Season 3: More Out of Order episodes, and Executive Meddling spurs the head producer (Tracy Tormé) to leave and be replaced, which leads to more 'action-oriented' episodes (that were just copycats of movies currently in theatres). Then mid-season, John Rhys-Davies is fired, his character replaced with a Ms. FanserviceAction Girl. The series is cancelled yet again, but this time brought back by a Channel Hop to the Sci Fi Channel, but not after a year off the air. During this time, Sabrina Lloyd decides not to come back. (There were rumors she didn't get along with Kari Wuhrer, but the fact she was now working on Sports Night meant she would have to juggle two production schedules if she did return.)
Season 4: The Sci-Fi Channel executives wanted more of a focus on the Kromaggs, leading the show even further from its original premise. Then came the aforementioned "Hire My Brother" decision, with Jerry O'Connell also taking over more of the writing and changing his character to more of an Action Hero. However, the Sci-Fi executives eventually started letting the show get back to its original premise, and it was becoming decent in the late fourth season.
Season 5: The O'Connell brothers decide not to come back for the fifth season. This, combined with the budget going down to almost No Budget, doomed the show to cancellation after less than a month from the fifth season premiere. The ratings towards the end were actually pretty good, normally enough to secure another season, but by the time the show had made it to the finale, commitments for other shows had already been made.
Un-Canceled: Twice. Season 3 happened because of a fan campaign, and Season 4 happened by way of a Channel Hop. (Several sources listed the show as canceled after Season 1, but this was not officially the case.)
The major arc of Season 4 had a far different ending in mind. Originally, the team was supposed to make it to Kromagg Prime, where it would be revealed that Colin was unknowingly The Mole, an altered clone of Quinn created by the Kromaggs. The Sliders' Season 4 quest would have been a Kromagg deception to re-conquer their home Earth, with it also being revealed that Earth Prime had never been conquered at all. The Kromagg plot was hinted at several times, but the plot was largely dropped due to resistance from David Peckinpah. With the final resolution aborted, the arc was altered and the related loose ends fizzled.
Tracy Tormé intended Ryan to be apart of the team for a few Season 2 episodes, creating a love triangle with Quinn and Wade.
John Rhys-Davies was contracted for the entire third season and would've stayed if not for the behind-the-scene bitnerness. Scripts for "Sole Survivors," "The Other Slide of Darkness" and "The Breeder" were being worked out before his departure. A script for "Sole Survivors" with Arturo is available here.
Logan St. Clair was intended as a recurring nemesis.
"In Dino Veritas" was conceived as a mere Bottle Episode, but Jerry O'Connell was allowed to film his part in Jerry Maguire and the special effects proved to be more elaborate than at first thought.
Production intended to bring back Bennish for Season 5, but the cost of flying Jason Gaffney in and out of Canada was deemed too large.
ABC was contemplating a version of this show called "Doorways" before a shuffling of upper management caused its main champions to jump ship (and, evidently, end up at FOX). The guy developing the pilot for them? George R. R. Martin. (source: here)
Even after it was a given that Jerry O'Connell wouldn't be back as a regular for Season 5, he was willing to return for guest appearances to allow Quinn to be written out effectively. Reportedly, the deal was for six episodes, but a sticking point for Jerry was Charlie. It boiled down to Jerry wanting his brother in for all of Season 5 and production refusing - so the deal fell apart.
After Sci-Fi picked up the series for a fourth season, Tracy Tormé made a play to return as executive producer. (Fellow co-creator Robert K. Weiss was also interested in getting back in the game.) This didn't happen because the studio was contractually obligated to keeping David Peckinpah onboard. Tormé couldn't stand the thought of working with Peckinpah again and couldn't convince the higher-ups to remove him. This interview features some ideas Tormé had in mind for Season 4, as well as other parts of the show's run.
The idea was thrown around of revealing that Maggie's biological parents were Colonel Rickman and her universe's version of Wade (this would have meant Maggie's universe was in the future compared to ours).
There was a proposed episode that would have shown what happened to Wade after she was taken to a Kromagg breeding camp without Sabrina Lloyd having to return to the show, via the gang coming upon a device that made them experience past events from the perspective of other people. Maggie would have been Wade, Diana would have been Mrs. Mallory, Mallory would have been a Humagg soldier in love with Wade, and Rembrandt would have been a sympathetic Kromagg scientist.
Fox wanted to renew the series for a fourth season but it would just feature Quinn and Maggie alone. This is why season three ended on the cliffhanger where Rembrandt and Wade slide back home with Quinn and Maggie following but ending up in a different dimension. This plan ended when Sci-Fi decided to pick up the show.
Word of God: The creator has gone on record stating that the world mentioned in You Can't Go Home Again was actually the group's homeworld. He has also stated that the plot from Season 4 with Quin being from an alternate Earth was up until the season finale going to turn out to be a hoax by the Kromaggs. This concept was abandoned when the budget dried up and the intended master reveal of Colin turning on the group due to his status as a sleeper-agent-modified-clone-of-Quinn and wormholes opening with dozens of Kromagg ships pouring onto Earth Prime due to Quinn opening the Slidecage was no longer feasible to film. Several fanfics have taken this original plot and run with it.
It's also been stated that the wrong Arturo slid and that there were several hints placed that showed this.
Confirmed by Tormé himself, after over a decade of keeping silent on the matter, he considers the "Wrong-Arturo" from Earth-Double-Prime to have been the one who slid with the regular Sliders, thus the reason for the horrified "Oh my God" from the Aturo left behind.
This website compiled some very compelling clues years before Torme admitted the truth that, whilst far too long to post here, are incredibly compelling. I'll summarize for those of you that don't feel like clicking on the link that there was a lot of work involved in setting up the swap to the point it was obviously going to be a future story arc if Torme and Davis hadn't been fired.
If he hadn't left the show, Rhys-Davies probably wouldn't have been available for the Lord of the Rings films.
Written By Cast Member: John Rhys-Davies has story credit on "The Exodus, Part 1" (the episode where Arturo is killed off), though note that he had no input into the script. His original story bore very little resemblance in details and execution to the finished product. Played straight with "Way Out West," where the story originated from Jerry O'Connell (who by then was a producer).