I'd have to say this is my favorite in your collection, although it's hard to choose just one.
Critique-wise it's a very nice thing to see you using few lines. Most of your definition seems to be done with shading, color, and some texure.
It's hard to judge what your goal is - you know what style (realism, cartoon, somewhere inbetween or else?) My only real ~complaint~ is that you might try to blend the eyes, and maybe the mouth a little more into the same type of form the others have. The teeth feel 2d.
I'm not really sure what my goal is... I guess my "style" consists of not using outlines and my goal is to make high quality fan art for this wonderful show. Anything else is subject to change on a whim. I admire the works of tsitra360, ponykillerX and Matt Kohr. So I guess my aim would be some mixture of those three styles. Or something like that hell I don't know.
Hmm...when I look at it, it seems to be really successful. And it indeed is! A nice alternative to your previous maybe overlighted work, this one really stands out! A perfectly filled work with lot of detail (the... glass (I don't know how it's called in English, probably not glass) - I love how it turned out, especially the "hand" - it really looks great + it's the most detailed thing in this drawing). I like their expressions and the situation you put them in - it fits the contest perfectly.
The characters - they look very good, not sure if they are not too bright though (you know, it's nightime actually, but maybe this place is so bright, I'm not qualified enough to say that for sure). Shining Armor's horn is a little too broad in my opinion and the noses angles seems not to match the mouth angles perfectly (especially Shining Armor's mouth - it doesn't accent the shape of his nose), but it would be rather a nit-picking to point it out as a mistake. I think you should try to make the notches and the mouths more visible by increasing the amout of black in them, but that's only a suggestion of inexperienced human.
Do you know what I like most in those ponies except for the perfection of them? The light anatomy shadow on Cadance's neck - it looks so smooth somehow and so natural (I completely adore it)!
And that's pretty everything I wanted to tell you about this drawing. You did a great job on it!