Borderlands is a great game and I enjoyed it thoroughly. I’ve also played Fallout 1,2, Tactics, and Fallout 3; and as soon as I am done with this I’ll go back to Fallout New Vegas. I’m a fan of all of them.
Rage’s setting will be post apocalyptic Earth like Fallout, but with an asteroid strike rather than nuclear war. Borderlands is set on an alien planet.
Borderlands changed their art direction well into development in order to differentiate themselves from Fallout 3 and Rage:
“However, by October 2008, Gearbox knew it had a problem. Internal reviews by the "Gearbox Truth Team"--a group of testers with psychology backgrounds--concluded that people found that the game's art style was too similar to that of the then freshly minted hit Fallout 3. The game was also drawing comparisons to another post apocalyptic game from id Software. "We didn't want to be considered a poor man's Rage," said Martel.”
http://www.gamespot.com/pc/action/borderlandsthesecretarmoryofgeneralknoxx/news_6253257.html
I expect that Rage will not give on an over the top, almost campy feeling that Borderlands or Bulletstorm will. An over the top experience like Duke Nukem or Serious Sam.
Finally Rage will be on a brand new engine, rather than using recycled aspects of Brother’s in Arms: Hell’s Highway (another game I need to go back and finish). Id Software is one of the world’s preeminent game developers. However they have not exactly been prolific recently.