just dropped my car off for a look at the air con - and the dealer had a black gti with all the options (leather/ sat nav etc) in the showroom
looked great
, but very very similar to the mk 5 in many ways.
not enough difference to change for me, but would be on my shopping list if i did not have one already.
Can't wait for the R20 though- now that may be a reason to change 
There may not be that much visual difference, but that doesnt mean to say the car isnt different. I think VW intentionally didnt make many changes as the mk5 is already a exceptionally good car, but it is different and better....
XDS, ACC, better quality parts used for the interior and looks better inside, its a more smoother drive, more refined and higher torque at lower end plus better response, better car insulation, better power steering, more miles to the gallon, lower tax due to lower emissions, engine overhaul = new pistons, rings, vacume pump, fuel pump, air flow sensor, more bhp and faster ! (I googles the engine changes as i wasnt sure exactly), different exhaust layout, different lights, slight change to the 18" alloys, parking assist generation 2, cruise control is more adaptive on the mk6, there's a few more little tweaks here and there. Not huge changes, apart from arguably xds and acc, but they all add up.