Basically, Rage in it's current state has issues. So here's what I've come across for fixing it as much as possible, until we get better drivers and probably a patch or two from id.
Firstly, using the "Rage" driver from AMD does help performance, but it also won't allow crossfire to work. Still, my single 5850 with all the following tweaks runs a steady 60fps and doesn't even top out it's usage (sometimes as low as 40%). If you're using AMD card(s) and the game crashes at startup, you need to disable Triple Buffering in your Gaming options of CCC.
Ok, so first off, Rage is supposed to have a folder created for it in your AppData folder. You need to make sure you have this folder created (manually):
Once you create that, as soon as you launch the game you can check it, and there will be a 1gb cache file in there. It helps with performance and texture popping.
Secondly, there's Bethesda's blog commenting on how to make the game load bigger texture files (8k) as well as how to force vsync: http://forums.bethsoft.com/index.php?/topic/1236250-rag...
This drastically helps by making the textures as crisp as possible (though not what I'd consider HD by any measure) as well as fixing screen tearing.
Finally, probably the best fix is to create your custom config file which can include any of the above fixes (this one here has vsync and 8k textures). That is to say, the fixes say to add them to the launch options, but it's easier to just save them in a config file. You have to make the file yourself using notepad and save it as rageconfig.cfg inside the rage/base folder.
EDIT (Oct 8):
This is the best config file I've used yet, and it's easy to tweak. Just keep in mind you need to add the FOV, vsync, and skip intro variables to launch options as they don't get executed properly from the config.
P.S. In regards to the gameplay for Rage, it has a soft spot in my heart because of it's "fallout 3" style play (not that its a copy, let me elaborate).
Having to actually drive to the conflict (which in and of itself turns into a scene from Mad Max), then having to use strategy and careful ammo conservation, combined with awesome gadgets makes it a blast.
The ammo conservation is akin to Resident Evil 4. Bullets matter, of course you can spend cash to buy more and stock up, but the goal is for your mission reward + goodies to be more money than you spent on ammo completing the mission.
The driving portions are a mix of Dirt and Twisted Metal, for sure.
The feel of the FPS, weapons, etc is a throwback to Doom, and last but not least, the engineering specs (allowing you to make a plethora of fun stuff)seems almost Ratchet and Clank(y). Sentry bots, RC car's with bombs strapped to them, and decapitating tri-tipped boomerangs are just a few of the goodies.
Fun all around. A solid B+/A- effort on ID's part.
Yeah the gameplay is pretty good I'd say. Enemies use a fair bit of cover, but then if you kill a couple the other ones sometimes run away like "HE'S KILLING US ALLL!!!" and then you can shoot them in the back =P
Some enemies rush at you with knives/clubs/etc and will do rolls and quick dodges as they run which makes it pretty intense sometimes as they're hard to hit.
The driving parts are actually pretty fun. Super arcadey, but once you get used to it (and a few upgrades) it's actually pretty cool.