Sorry, I know this is an old thread but as it's in classics (and also interesting and very useful for ideas) thought I would add a few:
Loved: Seville, Granada, Bordeaux, La Grave (Ecrins, France), Drakensberg mountains (South Africa). In the UK have always like the Lake District and the Scottish Highlands and Islands, especially the far North West.
Liked: Girona, Besalu, Lyon.
Not awful, but disappointed by: Carcassonne (Cite is too much of a tourist trap - like a theme park and full of mediocre restaurants and tacky tat shops, impressive to look at from far away but not that nice once you are there. Thought Barcelona was a bit overrated given how many people rave about it.
As for the comment about Tenerife being "dull as ditchwater. Absoultely nothing to do of any interest whatsoever!"
Obviously depends what your interests are but the village of Masca and surrounds are stunning as is the whole of the Anaga Rural Park in the far North East of the island, wonderful walks in the cloud forests and the hike from Cruz del Carmen to the cave village of Chinimada is one of the most beautiful hikes I have ever done. La Laguna is an attractive old Canarian town with a mostly pedestrianised centre with lots of nice pavement cafes and restaurants. You can go up what is (I think) the worlds third highest volcano, Teide, there are also sunset trips with a glass of Cava and night trips for stargazing, trips underwater in a yellow submarine, swimming in tidal pools created by molten lava in Garachico, a huge water park (Siam), you can visit lava tube caves, go on catamaran trips to see the giant seacliffs and go swimming beneath them, go snorkelling with turtles or go dolphin and whale watching, etc etc - seems like a lot of interesting things to me?