I've been using the G27, and am generally pleased with it. I think the biggest issue is not being able to control the degrees of rotation on the wheel. More specifically, I think the default wheel setting has too many degrees of rotation. You have to crank the wheel a long way to get the steering input you're after.
I believe this is the primary reason we see so many people complaining that they can't catch oversteer situations, etc. They can't quickly dial in enough correction with a quick flick of their hands. I have probably driven 50 different real cars on racetracks over the years, and I have more problems smoothly catching oversteer in GT5 than I've ever had in any of the real cars. In real life you have so many sensory inputs...you can feel what's happening at the tires, attitude/yaw of the car, tires screeching, etc. Your whole body is telling you what your hands should be doing. That's ultimately what the game is
trying to do, but it's tough to simulate.
If the degrees of rotation could be finely controlled however, I think quick hands would come into play and really help with corrections. As it stands with the default settings on the G27, when I give the car a quick correction like I would in real life, it never feels like I've given enough steering input. I have to exaggerate my steering inputs to get the car to react with some semblance of reality. In other words, if I normally would move my right hand from 3 o'clock to 12 o'clock when dialing in a little opposite lock, I intentionally try to crank in some extra lock, going from 3 o'clock to 9 o'clock with that hand instead. This works sometimes...but other times doesn't seem to be enough, or it is too much and will send the car into a tank slapper (or spin). It's imprecise trying to guess how much extra lock to overcompensate with. In a real car, on a real track, with normal radius turns, you never really have to move your hands from their 3ish and 9ish positions when counter steering (unless you're either spinning, or if you're an autoXer who just likes shuffle steering around super tight turns.
).
I know Fanatec solved this issue by having the degrees of rotation independently adjustable of the game on the fly. That is the ideal solution in my opinion. Unfortunately, I didn't want to deal with all of the horror stories about customer service, quality, etc. that go along with the Fanatec products (based on my research, not personal experience). I'd rather have a pretty good driving experience all of the time, rather than a really good one on the few occasions when you can make it work!
I think allowing that single adjustment would take the experience with the G27 from being pretty decent to far more fun and realistic.
