For me the biggest problem with the MK6 is that it's so similar to the MK5. Take the headlights / taillights and bumpers away, then it's pretty much just a MK5.5. Not to say that's not good, I absolutley love my MK5, it's just that my local dealer has been trying to get me out of my MK5 and into a MK6 for some time now (as they do), and to that end they twice ended up giving me a weeks loan of a GTD and a TSI 160.
Now whilst it would be stupid to say that the MK6 isn't a little better or the quality of the interiors hasn't improved, it certainly has, but after a day or so of drving it, it just felt like I was in my MK5 (just a little better and quieter). Maybe the MK5 is a hard act to follow, don't know. What I do know, is that if I'm going to be parting with £15-£20K on a new car, I don't want it to be 80% exactly the same as the one I've been driving for 4½ years. I want it to excite me all over again with little styling tricks and new things to find out all over again.
Just my 2 cents worth.