When Quinn slides from the astroplane into the
next world with the others, shouldn't he have
arrived still invisible on the other side?

Arturo claims that the vortex will remain open
for 60 seconds...but it remains open for
3 minutes

Remember the town at the beginning of this episode? The sliders walked along the street there. Well, that town looks just like Steveston, British Columbia, just south of Vancouver. And all this time, I though Sliders took place in San Francisco. Silly me.

Quinn Mallory's incorporeal state denies him to interact with any substantial objects, including of course people, yet he can still walk on floors and rest on automobile seats. This episode would have been much more fascinating if Quinn Mallory encountered the soul of his father, thus implying that he had all along been existing on the ethereal plane of the afterlife.