The only thing I miss from my R is the fender sound system. The b&o system is just too flat without a sub. Otherwise maybe just 1 or 2 minor complaints. I feel like the DCC on the R had a softer comfort mode and a stiffer race mode, but now that I think about it I honestly don't know if I've driven in comfort mode yet. The suspension on the RS3 feels better to me either way. There's way less body roll around corners. I noticed that pretty quickly going around my first corner. Surprisingly seems like visibility hasn't changed much, it's still pretty similar to a hatch. Oooh and here's one...The amount of engine rock on my GTIs/R always bugged me, but that's something I don't notice at all anymore. I'm happy just putting around and listening to the motor. 5 cyl farts are also magical like unicorn farts. I don't have any rattles I can complain about. No mechanical or electrical problems I've noticed. Everything's been perfect for me so far.
My only complaints would be things like the drive mode not being saved when you shut the car off. There's a couple modes it'll save, but in almost any other mode it'll default to auto when you turn the car back on. Some of the stuff on the gauges doesn't save either so you have to cycle through with the steering wheel to get to the info you want to see. The other would be not being able to keep the dsg in M while in D. If you don't shift for 10 seconds or so it'll revert itself back to shifting automatically for you. The only way it stays in M permanently is if you put the dsg in Sport. Sport just seems a little aggressive for daily driving. It brings the idle up to 1100 instead of 800, and I've noticed it doesn't disengage the clutch when you press the brake in enough at a complete stop. I haven't looked it up to see if I can change that at all yet. I've just assumed it's the way it is. I've always had manuals so this dsg thing is still pretty new to me.
It's a fun car though. It gets a lot more reactions from random people than my R did. People love seeing it, but I think that turbo blue has a lot to do with it.