There is a problem with the way people go about making fan films. It's fine if they want to have fun and be silly, but if they're trying to make serious-looking productions, they need to be more careful.
First, they need to put aside their geeky fantasies. You are not going to get any actor to come in and be Shatner's Kirk or Nimoy's Spock. They need to get away from impersonators entirely. This means either a complete reboot (which also means reimagining the look and feel of the project) or go with entirely new characters.
Second, they need to stop casting themselves in these projects. This is where fan films and serious films can't work together. It's hard enough to do this properly with original work and experienced crews. Doing it on a fan film level makes it impossible to make the film properly. They're putting themselves above the material, and that's going to kick them in the ass.
Third, they need to stop trying to recreate what has already happened. Stop using actors who are supposed to be other actors. Stop using actors who have been on the shows before, playing the same characters. Stop using the sets that look exactly like the other sets. Stop giving us reasons to look at the project and only see what they're not.
There is no reason why a fan film can't look great and feel great. There are perfectly good actors in most places around the country. Cameras today make it very possible to make professional-looking films for cheaper. But the project needs focus. Is the goal to have silly fun, LARPing these characters? Or is it to make a movie that looks like it could be the real deal?
Sliders... I was kinda joking about making a fan film, but it's not impossible. However, the rules still apply.
Step one: Give up on trying to look and feel like the original. Even if we could, the original is dated by today's standards. The methods used to make such a crazy idea look and feel realistic are completely different today. Mostly because we can have steadycam shots with CG work done a lot more easily today than we could have twenty years ago. The project would have to be looked at like a new film/series, creating the look and feel from the ground up.
Step two: Recognize and embrace the limitations. If you don't have Jerry, don't have Quinn. This would probably lead to a complete reboot of the series, or a sequel series that exists in the same tv universe, but follows different characters. Either way, don't pretend that your next door neighbor is Quinn just because he has a flannel shirt.
Also, if you don't have the ability to shoot big action sequences or crazy looking worlds, don't write them. Having the Sliders land in a world that's one big forest would look better than having them land in a crazy alien city that looks like a five year old made it with construction paper and a glue stick. Know your limitations ahead of time and write toward them.
Going back to my Buffy season 8 (because it's my big fanfic experience, not because I think it's the best thing ever), I built limitations into the story because I didn't want to write everything that I personally wanted to see happen, like most of the fanfic was doing at the time. I wanted to make it seem like a real TV show, so I thought about what a season 8 would look like. Huge budget cut, meaning a relocation for filming. A cast that was tired and wouldn't want to do 22 episodes. Characters who were dead and needed to stay that way. Others who wouldn't be on board with moving to Canada to film. Once you decide where the walls of your creation are, you can start decorating inside those walls.
Odds are, a Sliders fan film would be done with a few unfamiliar actors, playing unfamiliar characters, with few outdoor shots and a lot of interiors of homes, etc.
With those limitations in mind, I think a good product could be made. But I think the fan side of it would be let down by not being a new episode of the series, with all of the familiar characters.