Excellent wallpaper! The best I've seen since, ermm... ever! Now, I'm not a professional critic, and I have never provided a critique before. But I'll try my best to give you a good critique.
Vision: I like how you used Twilight's surname (Sparkle) as a pun for the title. However, this pun has been used a couple of times before, so it lacks a bit of originality. I also like your idea of adding lights and flares here and there in the background to make it more vivid and alive, and to make it more relevant to the word "Sparkle". This Vision is great, and it got 4 stars.
Originality: Like I said before, the pun is not that original. The idea of making Twilight "Sparkle" doesn't surprise me and I have seen this sort of theme before. However, the way you made the background so sparkling and vivid is very impressing and clever. I don't think that I have seen a wallpaper of Twilight before with a background that catches my attention. The Originality isn't that great, but it got 3 stars.
Technique: I LOVED the technique you used to make this. It's genuinely exquisite how are the visual effects are well-made. I find it very pretty and eye-catching how you knew to focus on the subject (i.e, Twilight in this case) and make her stand out in the photo, and maker her "Sparkle". Your technique is not flawless though. I think that it could have been better if Twilight was a tad more transparent so that we can see the background behind her. Overall, it was excellent and still got 4.5 stars.
Impact: This wallpaper had not surprised me because it lacked a bit of originality. But it managed to catch my strong emotions towards it with your good vision and excellent technique in making it. I think it would be worth saying that Twilight is my most absolute favourite pony !!EVER!! And that, of course, means that I'm overall truly blown away with the incredible background. This impact gets 4 stars.
So then I suppose if I had to give an overall rating and my general opinion... Rating: 4 out of 5. Opinion: True Masterpiece.