Well, let me start this off by saying that this is SPECTACULAR work. Hands down, this is one of the greatest Rarity pieces I've seen the whole time I've been a deviant [all 1 month ]
I'll start off with the things I DO enjoy about it, because not only is that what I usually enjoy starting with, but it far outweighs the cons.
The first thing that really caught my eye about this piece was Rarity's mane and tail. I simply HAVE to commend you on your brilliant use of lots and lots of lines to represent each individual hair; the style makes the entire work look so fantastic. As well as the individual hairs themselves, the single lighting source on them is very nicely done, because it gives the mane and tail a smooth look, so to speak; it doesn't look shaggy or unkempt, but rather neat and well-groomed, just like Rarity would do One last thing about mane: I love the little touch you added with the little tufts and strands of hair coming off from the top of her head; they accent the mane and make it infinitely more realistic.
Aside from the hair, I loved the detail you put into her head. The way you drew her mouth and horn suggest an almost 3-dimensional view of Rarity, which I love, being a deviant who specializes in ponies in real life
Aside from that, the shadowing is very accurate, the detail is astounding, and you added in a couple of creative touches like the faded blush and the small librarian glasses.
Well, now that I've told you everything I DO like about it, I do have one or two thoughts on how it could be made even more breathtaking. [Keep in mind that most of the suggestions I have, I only noticed when I looked at the full-resolution version; to most deviants, this would hardly make any difference at all]
First, your lighting is a bit inaccurate. The first light I noticed was the one on her tail, because it is the biggest and has the most contrast from the colors surrounding it. When I saw that I established the idea in my head that there was some sort of light coming from somewhere off to the right-hand side of the scene, off screen somewhere. When I saw that light, I looked around, and some of the shadows and other lights seem to be coming from other sources, yet they are unaccounted for in the shadows, and make the lighting seem a bit.. Off, particularly around the drop shadow on her tail [the shadow on the ground]. Like I said, it's not immediately noticeable until you're looking for it, but in a critique, we look for it
Another thing I would have improved on a bit: the shadowing, although relatively accurate, looks a bit unrealistic in full res. The thing that makes it seem a bit unrealistic is how there is both an unfeathered shadow edge and a feathered shadow edge in the same shadow. This mismatch in shadow opacity makes it look a tad bit awkward.
One last thing, and probably the least significant: The background choice seems off to me. It's one of those things where it's not anything you did wrong, it's just something that I personally dislike, because bubbles don't really seem like Rarity's thing
Well, that's just about it. You've done an utterly magnificent job with this, and aside from a few simple mistakes, it's damn near perfect, if you'll excuse my language.
Don't stop doing what you're doing, man, because you've got a gift for this.
Oh my, how I love this picture! And it's not just because my favorite pony is Rarity, no, it's because it is very aesthetic, and the art style is just something great to behold! The facial expression on Rarity may just be what sells it though!