I love them as an idea. I wish the Barcelona local government would understand the simple concept of contraflow bike lanes on one-way streets.
Instead they keep building more and more two-lane cycle paths on either side of one-way streets, fully segregating bicycle traffic from motor traffic. While they surely believe that makes it even safer for cyclists, in my opinion it is a terrible (and less safe) design for multiple reasons.
Firstly, it continues to encourage the idea that cyclists are second-class parts of urban traffic, who may use the streets when by the benevolent grace of the Barcelona local authority they have been provided with their own mini-street on certain grown-up car streets.
Secondly, having to divide the dedicated bicycle space in two, one for each direction of traffic, increases the risk of bike collisions and makes overtaking slow cyclists more of a hassle.
Thirdly, it often makes cycling from A to B harder than driving if your route happens to follow the "standard" direction of the one way street and you need to make a turn to the side opposite the side where the cycle lane happens to be. This forces you to cross the ordinary one-way motor traffic lane, which you wish you were using in the first place, with the added difficulty that the cars are coming to you from behind.
Finally, it really messes up with the crucial factor of predictability in road safety. So many dual-lane cycle paths on arbitrary sides of one-way streets make each intersection have its own personality, and you'd better hope the drivers you'll encounter are locals who know to expect surprise bicycles sprouting out in the opposite direction on their right-hand side. While one could argue that contraflow lanes also mess with predictability they do not, for the simple fact that traffic continues to follow the standard logic of circulating on the right of the road.