Basically the new game adds Towns as a new tile (the red ones) which have some bonus functionality. When you play a red tile you can build on it from the options behind the big hand in the photo above, and the different buildings offer different victory points bonuses.
We only played one game, so that might be a factor, but it did seem to slow the game down slightly – one of the great things about KD is how quick it is to learn and how quick to play. It does add a couple of years to the minimum age/intelligence needed to be able to play as well, so if you want to stick to an easy game or play with very young folk then stick to KD.
However, the extra tactical stuff was good fun, the scoring sheets (very similar to those in 7 kingdoms duel) were useful, the different way of playing 3 players was a good idea (discard the unused tile), and I’m looking forward to mixing QD with KD for a 5 or 6 player game, so very happy with the purchase!