The amount of detail is pretty amazing to look at, I won't lie. However, the amount of detail seems rather unfitting with the vector used here. Vectors don't have a great amount of detail - in this case, we have an outline with solid blobs of color. Wild Fire looks very out of place in a world with so much detail (especially with that 3D model you used for the mountain).
I draw my ponies with a level of detail that is a higher level than a regular old vector, but there are times where I look at my work,and tone down the level of detail. I've learned from personal experience that details do not always add to an art piece. It's pretty much the point I would bring up to this critique. I believe that future wallpapers you make might feel more coherent (for a lack of a better term) if you tone down the level of detail.
Would your future wallpapers look better with a lower level of detail? Well, only one way to find out!
Details aside, I thought it was very weird having Wild Fire stand on a mountain looking down to Canterlot. We all know Canterlot as a place that is really high in the mountain, so I felt that her placement was a little silly. xD Not sure what other people feel about this, but it came off to me as weird.
Yeah, I'm an art student basically majoring in Visual Effects/Motion Graphics, so I tend to favor these things a LOT, combining special effects with both 2D vector art and 3D Modeling art (the mountains you see in my wallpapers are 3D Models I make from scratch)
Of course, I'm going to be trying out a few new styles and techniques in the near future, as I try to mix it up, and try new things whenever possible. ^_^
Well, when I draw ponies, there have been times where I look at my work and decide to tone down the level of detail I put in my hair. The art style of ponies we've grown an emotional attachment are simple vectors; details might not help us all the time.
Doesn't seem a bit strange that you have a simple vector - something that's basically an outline with solid colors, but you have a great level of detail in your mountains? I dunno if toning down the level of detail would actually help (maybe it wouldn't), but who knows?
Just my two cents. Too afraid to put that in a critique as it would attract too much attention