They are brilliant, and it takes a lot of willpower not to have the exhaust in noisy mode everywhere (though I also appreciate that it can be quiet when you have to start it up on a morning!). It really is quite thirsty, but I guess that mainly depends on the kind of driving you do.
Have a good play with the custom settings. It's one of the best things about the car, being able to switch from a "daily" mode like Eco or Normal into a perfectly-tailored more focused mode in Custom. As I mentioned earlier the regular "N" mode is a bit too silly for the road - the ride is pretty bad and the steering too heavy - but you can find a real sweet spot in Custom.
Make sure you drive it somewhere fun at some point too. UK roads totally don't do justice to the way it performs, but I took mine to Rally Germany earlier in the year and it was mega on the mix of twisty stuff and autobahns. My parking space wasn't bad either