I mean, wow.

The concept was pure science fiction, as in what it did was allow the writers to push the characters into whatever they wanted to, really.

And like all the best science fiction, as they jumped form dimension to dimension, the writers picked a philosophy, a political side, a religion, a cultural issue, an economic issue, wrote it to an exaggerated extent, and examined it...

... and then moved on to another, and another, and another.

In short, it was created to do exactly what SCI-Fi was meant to do, and that is why people love it. PURE SCIENCE FICTION. You can literally compare this to the Twilight Zone and it would be apt.