The light is fantastic. The glow on Twilight's fur is beautiful and balances well with the surrounding ethereal plane. The repetitive circles of light give a good effect, almost as though they're framing Twilight in the drawing.
The feathers in her wings have good detail. Starting small, they become longer as the wings span out, and even give a sense of layers, as is indicated by the light and dark values.
Twilight's expression is also pleasant. The direction of her eye and the way her ear is bent is quite endearing. Great body posture, too; very fluid. Her snout probably could've been given a bit more attention (or perhaps just a tiny notch to indicate her nostril), but otherwise it's a very well drawn portrait of our newest princess.
I had a lot of mixed thoughts when I first saw Twilight's transformation. I was happy for her, but strangely empty. Learning that this was Twilight's destiny, which had been planned for who knows how long (perhaps when Celestia first saw her cutie mark), I was afraid of where this wonderful show would go from there. But I think that was to be expected.
When things change, we often have worries of what lies ahead. We don't know what to expect or how to react when the future comes, but after some thinking, I've realized that that's okay. We all have those moments in our lives where we face a change that's beyond what we expected. As brilliant as Twilight is, I don't think she was expecting to be given her own wings, let alone become a princess. But it's as she said, "Everything's going to be just fine." It's important for us, in our own lives, to believe the same. Yes, in life there will be challenges ahead, and some may shake us to our very center, but with a strong spirit and good, caring friends by your side, there's no change too great to face.
When I watched "Magical Mystery Cure", I was afraid Twilight would change drastically after she was crowned, that her personality would be altered and that her title of princess would prevent her from being with her friends. But now that I think about it, it's actually kind of silly for me to have thought that. Yes, things will certainly change, but Twilight's personality is still hers and not controlled by the crown she wears. She has come a long way and has grown so much, and she understands just how important it is to have friendship in her life. You're absolutely right — the idea of her growing apart from her friends would be contradictory to all the adventures she's had and all the tests Celestia has put her through. If anything, I think it will be crucial that Twilight keeps her friends close as she and they all enter the next chapter (or Season) in their lives. Twilight needs them just as much as they need her.
I look forward to what awaits in Season 4, and I pray that Twilight becomes all we hope of her. I have no idea what lies ahead, but then again, does Twilight or anypony else?