[Glathannus]

I prefer her earliest vocals as a signed EMI artist, because the quirks were one of the main things that set her apart from other vocalists. I'm not a big fan of the Dynamite Out version of Koko de Kiss Shite not because the vocals were 'bad', but because the quirks aren't there. On the otherhand I don't like the way the single/album version was produced. So for me the best version is the demo you can find as a bonus feature in Baishou Ecstasy. It's quirkier vocals with less distractions.

I also like many of the demos that don't have videos, mainly for their quirks.

Now I wouldn't go so far as to say that her quirky vocals are her ONLY good vocals. Kokoro (especially on Dynamite Out) is a very solid performance that I couldn't imagine hearing from a younger Shiina Ringo. Plus for an album like Adult, it's better that the vocals aren't quirky.

I don't think she's "losing it" with her vocals. Her vocals are simply changing not necessarily for better or worse. What's more important than whether or not her vocals are quirky, is if she's putting her modern vocals into a composition/arrangement that fits well with her vocal attitude at the time.