While I'm being Mr Grumbly, here a few of my unfavourite things.
Entrances to and exits from cities that go all around the houses (see Eindhoven, where the marked route to the city centre was as bad as some of the cycle routes I use to loathe into the centre of Oxford). Once you've got to the outer ring road, just find an arterial road and follow it to the centre - and vice versa for the exit. That's the utility bit of the ride - the fun starts in the countryside.
Sterile forestry plantations with no wildlife, especially ones where the cycle path is either completely rotten gravel, fit only for mountain bikes, or is a narrow single-track bit of blockwork which turns a ride into a procession. On the other hand I love a bit of heath, especially since it's rare in the southeast of England.
Bike paths which turn through right angles (see the forest track on the ride in to Breda). Even on a solo bike, but more so on a tandem, once you've slowed down to walking pace and hauled your bike through 90 degrees you're knackered and don't want to do it again in a hurry.
It's human nature to remember the salient points of any series of events - you remember the beginning and the end and the high- or low-point, and form your impressions based on those. Hence Bruges to Ghent was marvellous (high-point - Gekke Fietsen) while Eindhoven to Breda was grim (low point - forest outside Breda). It's worth making sure that potential low points are balanced by potential high points to get around this.
Yes, I know the answer is to get out there and organise my own routes. And if I manage to find a congenially part-time way of earning enough money to support the lifestyle we enjoy I will. This is in the spirit of constructive criticism to turn what I thought was a marvellous couple of weeks into a fantastic one.