This was a very pleasant surprise.
Normally, idol shows have an idol plot and that's it. But this one has a plot by it's own, outside of the idol thing. It is a mystery sorrounding a crime in which a robot killed a human. And with that premise, they did a veeeeery good story involving everything they show us in every episode (so, in the end, there are no filler episodes, even if you might think that way ).
The songs are amazing (and obviously they had to be, because Elements Garden is behind them xD) so not just the main plot is good, the music is also good. And if you like the anime, there is a game that apparently starts just when the anime ends so... great!!