Ok, so, just came back from seeing this in the theater in 3d (got stuck in traffic & so missed some of the fantastic opening number!
Anyway, my impressions:
In general, very well done. The one thing I went in concerned about with the conversion was indeed an issue... with the cell animation, much of the content that consisted of large patches of identical, unbroken color tended to "flatten out". In other words, if there was a good deal of shading or gradient, your eyes have a point of reference and objects seem round and fleshed out. Unfortunately, with traditional animation like this, there is quite a bit of solid color content, and most of it is in the foreground characters (moving figures tend to get less shading than static objects, as it makes for more fluid motion). In this sense, background elements and scenery worked better in many instances.
Things that also worked well included jungle scenes, scenes with expanses of grass in the foreground... basically anything with multiple layer elements moving across each other. Stylized scenes (such as the musical numbers) were also very effective.
I don't know much about how they approached the conversion process, but seeing as how the elements were originally loaded into the digital realm for coloring, it's possible (seemed probable from what I saw) that they had different layer elements already separated, and this could have accommodated the work done on creating depth (meaning they wouldn't have to generate content that wasn't there for the second eye view). There were many scenes with movement & panning, and at no point did I spot any artifacts that seemed related to 2d-3d conversion.
I specifically watched for the color timing, since there has been talk on these boards about tinting or recoloring. First off, the zebra stripes in the "Can't Wait to be King" number lean toward green, as in the screen shots posted, rather than blue/gray. In that sense I think this is good, since the blu-ray seems to match the theatrical release, or at least this latest master. Now, whether it matches what went to print in '94, I don't know, but at least we're getting something consistent with what's on the big screen now. Keep in mind that the number is very stylized, though, and I can tell you the zebras fit right in. Stripes elsewhere in the film were definitely black/charcoal gray, so definitely an artistic choice.
The water in that same scene was turquoise. Simba & Nala's coats were discernably different from each other, but not drastically so; certainly closer to each other than the screen shots from the dvd.
Aspect ratio looked to be abut 1:78, but honestly I don't know if I could have spotted the difference between that and 1:85. I won't comment on sound (let's just say it was not fantastic)... but the theater I went to was an older, art deco affair, so it was probably the venue.
In any case, I did enjoy the evening, and I will be picking up the blu. YMMV, but I hope these comments were helpful.