This series (or rather series of series perhaps) started out so strongly in season 1. We were intrigued. The actors and acting were strong. The storyline different enough to be worth watching and wondering what direction they were taking. The four episodes of the short season were just about right. I'd give season 1 maybe an 8 out of 10.
Season 2. Still good though it did seem to wander a bit. A new storyline set somewhere else in Spain with a couple of new characters to add to the mix that made it interesting in its own way. Not as good as season 1. Not as satisfying. A few scenes included that we wondered what the point was. But still watchable. Down to 7 out of 10.
Season 3. What on earth is going on? It just seemed to wander aimlessly from scene to scene and episode to episode. At times, it seemed to be liking a Sartre play it was so odd. Scenes seemed to be added just to make up time and fill in an episode. Characters introduced with their own stories only to never be head of again. The final episode had a 10 minute drug induced sequence towards the end that was just bizarre. It was all quite painful in the end. 5 out of 10 would be generous.
Season 4. Well, we didn't watch the two episodes that made up season 4. I took a look at the IMDb reviews and noted that the final episode was scored 5.3 by other viewers. That said it all for me. We chose not to endure any more pain. Thank goodness the writers realized that enough is enough and no more will be made.
I hope that helps other viewers. Season 1 definitely worth watching. Season 2 if you are huge fans of the actors. But leave it at that or you'll be left with bad memories of the whole series.