Pretty different. The Bethesda editors involve snapping together various building blocks to make structures which makes it fairly easy to throw something general together that looks good but also limits you to the building blocks available. I assume RAGE requires that you custom build everything and then apply textures - this gives you much more freedom and doesn't require 3D modeling software to make new components but it does make world building more complex.
From the Quakecon videos a couple of years ago, They still have a traditional FPS level editor, which is kind of like a stripped down 3d modelling app, but you're not likely to build anything that looks as good as the retail maps with it. I believe most of the maps being created for retail are being built almost entirely in a professional tool of one form or another, exported, then imported into the game editor for texture stamping, entities, and other game-specific stuff.
Luxology posted this screenshot of the Wellspring map in Modo a year or so ago:
http://www.luxology.com/community/blog/images/ws1.jpg
Anyway, this is why they've made a couple of attempts to let people know that modding will be pretty hard for Rage. It's not because of any peculiarities of the engine, but because the greater the complexity, the higher the level of entry. If you want your levels to look as good as the stuff in retail, you're gonna have to be really, really good, and really, really patient.
You can probably still make some pretty good looking stuff with the game editor, but I'm not sure if you'll be able to do the crazy detailed geometry like you see in the cliff faces and stuff unless you're using a full fledged 3d application.
In the Quake 1 days, big mods would take a few months to release. Doom 3 and Half-Life 2 mods took 3-5 years or more. It's not getting any easier.