Now, to the important stuff: Why do I like this so much?
Simply enough, it explains why Suigintou is the way she is. Haven't you watched or read enough things where there are incredibly evil antagonists, and you hate their guts, but you have no idea why they're doing what they're doing?
Suigintou starts to change in Träumend but as viewers we still don't understand where her attitude comes from. Those who have watched Rozen Maiden will know why Suigintou's particularly sensitive to certain insults, but Ouvertüre tells us the real reason, and I am inclined to believe even Suigintou-haters will empathise (or at the very least, sympathise) with her, even if only for a fleeting moment.
And even though the events in Ouvertüre take place before both Rozen Maiden and Träumend, I highly suggest watching Ouvertüre last to fully appreciate it.
In other news, the art and animation's wonderful, and as for "sound", I tend to weigh the seiyuu's performance more heavily than the music. Both Tanaka Rie and Sawashiro Miyuki (Shinku's seiyuu) were outstanding in Ouvertüre. And I'm not kidding about that at all. I don't think it's possible to watch Ouvertüre and come away thinking, "The seiyuu could've been better than that."
I do wish it were longer-- for how can two episodes sate the insatiable? -- but I think it's a suitable length for Ouvertüre as far as things go. The point of Ouvertüre isn't to answer and explain all the unanswered questions thus far; it's to give Suigintou character development.
And in that regard, I think it's succeeded in a most spectacular fashion.
