I can probably sum this review up in 3 words: Needs another season.
The story is probably not the strongest part of this show, but that's not a problem as the reason for that pertains to plot holes that could be filled with another season. The revenge aspect of the plot is a generic plot element that wasn't really brought up to an obsessive degree which is good becaUse I would've gotten annoyed by hearing about it in virtually every scene.
The art and design really stands out to me, as I like how they used a steampunk style setting and used that in the
majority of the series. The one gripe I do have about it was the jarring transition to CG animation during certain scenes, namely the action scenes, but the CG animation itself was utilized very well, it was just the transition that was the problem for me. The character designs were very intriguing and, at least to me, felt fresh and unique at no point did a character stand out unnecessarily and felt out of place to me.
While the opening and ending were probably my favorite ones from the entire year, the opening because of how awesome it was and the ending cause it was catchy as hell(Spin Spin Spin Spin Spin), the soundtrack stood out very well. I like OSTs that know how to set the mood and for me, UMD's did just that. Two songs in particular were really good and definitely worth a listen to outside of the show, Magica and Bravery Steps(you'll easily notice them if you look them up), and Bravery Steps is probably one of the best instrumentals I've ever listened to.
This is probably where the best and worst parts of the show lie. While each character is easily likable. They also have ticks that will annoy you if you don't like seeing that kind of thing in a character. Yaya is probably the character that'll cause the most division between viewers as while she's a great supporting main character, her excessive(sometimes bordering on obsessive) loyalty towards Raishin is both a good and bad trait as while she has her moments where her loyalty is tested and that's great to see, her constant attempts to, for lack of a better phrase, get in Raishin's pants, tends to get annoying.
Unbreakable Machine Doll is a good series, it is well worth a watch and at no point was I ever bored by what was going on. Despite some parts that felt rush, it never felt like it was a hindrance on the series itself, the writers put out what absolutely had to be seen or heard and did it exceptionally well. Like I said there are a lot of questions left unanswered and only another season will help. If there isn't another season, then this show will be badly hurt by the lack of one.