The teaser is very intriguing. The content is strong with the idea of two sets of sliders on the same world, one evil, one from Season 4. Evil!Colin's behaviour is instantly disturbing.
I'd say that the main problem is the prose and perspective. The main content of your first scene -- the sliders emerging -- is just dialogue. And the dialogue is fine, but there really isn't any other meaningful information other than the banter between the sliders. Enjoyable banter, surrounded by prose that doesn't inform us about the characters or the setting or the atmosphere or the tone in any meaningful way.
This is not a unique problem in fan fiction. The reason this is happening to you: you are attempting to convert a set of television characters into prose, but your grasp of the characters is in terms of physical performance from the actors and spoken lines of dialogue, all from a detached third-person perspective. Prose, by its nature, requires delving more deeply, either in offering internal perspective within a character's thinking or in focusing on environment, atmosphere or exposition.
The only real way around this is to devise 'literature-friendly' versions of the characters and settings that are suited to the prose format -- or you could just say screw it and write a screenplay.
Or you just carry on as you are now, accepting that flaws and mistakes and material that isn't quite right is all part of the process of learning as a writer and even if this story isn't all you want it to be, you will grow from it. I can promise you that I will read it -- but right now, I have to go out, I have a hankering for potato chips.