What I Liked: Both the OP and ED. The fact this series practically screams "experimental" at times. The final act is quite nicely handled. Has a interesting mix of ideas and themes, using Pinocchio-style motifs to deconstruct Idol culture and hint at the intersection between mythology and science. Pacing is good, if not slow, until the final two episodes. Visuals are solid for the most part, especially when it comes to the robots, the cityscapes and the concert scenes.
What I Didn't: The fact this series practically screams "experimental" at times. Viewers may be deterred by the fact the last two episodes are both 90 minutes long. Episode 14 and the first half of episode 15 is just an incredibly clumsy feature-length info-dump. YMMV if you're at all squeamish - there's a fair amount of violence and disturbing sexual content. Key herself can feel rather passive to the point of annoyance, depending on your point of view.
Final Verdict: An interesting deconstruction of Idol culture, Key the Metal Idol is an ambitious experiment that risks being overencumbered by all its ideas. Sure, it's a rather pretty experiment with good visuals and an even better soundtrack, but the poor handling of the penultimate episode nearly undoes this nicely complex cyberpunk tale.