overall I felt the FFB was quite bad, gave me no feel for the grip and very loosey goosey with a G27.
I find the FFB pretty good, especially helpful in countersteer, I can usually just throw the wheel and it generally ends up where it needs to be.
Try setting the 2nd and 3rd settings in the Logitech profiler (or the device settings if you dont use it) to 0% [damper and spring effect], and disable the center spring and make sure to allow the game to change the settings.
I also found a lot of things annoying.
1. You need a handbrake, unless you can make your own makeshift handbrake you're screwed here because there aren't any wheels that come with handbrakes, I tried using the clutch pedal as the handbrake and it screwed me for the clutch and was weird. But you really do need one.
Thats something that should be pretty expected with a rally game, a lot of people use shifters they arent using, but theres plenty of cheap ways to make them if you also want to use the shifter for..shifting. Getting a handbrake lever from a scrapyard and putting a microswitch so its activated and wire it into a gamepad (or the O button on the G27 shifter, so you can also use it for GT5, if you wanted.) I have a crappy one made out of a broken flashlight and a springed clamp from a cheap car-fan. Really anything with a pivot and a spring with a switch (just google DIY handbrake and you'll get tons of cheap ideas.)
Also, RBR supports analog handbrakes, so just getting a cheap joystick and using it as a handbrake is an option. So either way, $5-20 and you can get a handbrake.
2. You cant change down gear when you want, you have to be in the right speed range before it will change and it isnt very lenient so often enough downshifts won't happen because the revs are tiny bit off, I find this annoying as hell as I use the gear changes to affect the way the car handles but this doesn't allow you to do it, so half the time I drive expecting something to happen as if I was in (for example) 2nd gear, but I'm in 3rd and I get understeer city. I've seen people using H-shifters, but there is no option in the game for this, nor can I find one in the 2011 mod so I was using flappy paddles.
People have already mentioned the H-shifter mod, it works really well, and also doesnt interfere with sequential shifting (so you dont have to remap when you want to change)
As for the other thing, In RBR's options, go to Gears > turn off the safety thing, then you can downshift whenever (if you have damage on, you can damage the transmission, but I dont so it got rid of an annoyance.)
3. Driving views are all terrible, the outside (bumper cam) view is a little off and I found myself hitting things because the edges are not what they might seem compared to other games. I found the incar views to be almost unusable, no bonnet view with the 2011 mod cars.
I just always drive in cockpit cam, and find the default view generally good (on the included cars at least) because my wheel sits right near my monitor. To get better views you can use camhack, but thats kind of annoying and you have to enable it every time you start the game and switch to the saved views. I generally just edit the setting ini for the car to get the right view. (for example \RBR\Cars\subaru1\subaru1.ini, find Cam Internal, the Pos part changes where the camera is [1st one goes left/right, 2nd one up/down, the last one with the negative number is forward/backward]) its a bit of a kludge, but you only have to do it once per car.