The syntax is unfamiliar to most, but it's very consistent and learnable. The syntax is one of many aspects of the design that keeps the whole thing simple. The use of a stack to pass arguments between words makes the kind of "pipelines" which are common in CLI shells very natural. I can think of few, if any, other languages I would want to use interactively as a replacement shell without complex line-editing assistance.

For those curious as to what a modern machine using Forth on bare metal as an operating system might feel like, check out Open Firmware: https://www.openfirmware.info/Open_Firmware

(If you have an OLPC sitting around in a closet somewhere from the Give-One-Get-One program years ago, you already have a serviceable and physically robust Forth machine ready to roll! Same deal for some older Powerbooks and Sun workstations.)