Only thing I don't like about the performance is the piano playing. I find it hard to believe that it's 2018 and people are still pretending to play piano for 30 seconds before standing up as it magically continues to play itself.
Yeah, I found that pretty tacky myself as another fan of the song. I liked the dark and intimate staging, and the pianos felt alright when they were actually being used... but as you said, when they walk off and there are still pianos playing in the background, it created a pretty laughable moment that broke immersion. And immersion is key in this performance.
Do note, however, that they abandoned the pianos for their reprisal performance, and hopefully that wasn't just because they didn't have time to set it up or something – perhaps it's a sign that they've already ditched that part of the staging? It might be a bit of a stretch – especially given that staging is one of Spain's weak points at Eurovision – but I'm hoping that it means they've already reconsidered and are looking toward a more genuine approach, which if done right could catapult them into a high finish in May.
...Assuming that the couple are still together then, of course. If they end up breaking up over the next few months and have to fake their romantic chemistry for the performance long after having lost that spark, then it'll lose that entire cute, genuine nature and just come tumbling down, I feel. Weird to think that a country's performance at Eurovision will depend on a young couple's relationship status