Missing some shading in some areas i.e. Rarity's and derpy's hind leg. But those are minimal mistakes.
I agree with dublinp on the "overall too bright" point, but I think he described it wrong.
Maybe if the gamma of the background was adjusted it would highlight the ponies (and Spike ;p) much more. So allow me to present a critique. Some of this is of personal preference but I'm sure there is much to learn here...maybe you already know some or most of this and were a little lazy with the pic by the end of it, but here are a few tips on how to make an image REALLY POP and I feel it's still informative to the community...so here I go. Reference/visual tutorial: http://i.imgur.com/R2ZEE2Q.jpg
I'd say make a curves adjustment layer over the background (I'm explaining this as if it were Photoshop) and output of 100 and an input of 150 for your blacks and take the whites down to about 225.
I fiddled with the image a bit myself and I found even adding 2 layers of lens flares; lower one (on black background of course) being of higher brightness with a 50% overlay and the upper layer being a less brighter, more focused flared with a screen at 100% right behind Spike, just peaking over the mountains.
I had to mask the ponies (roughly) when trying to add these color correction effects to the background which gave me an idea of even adding some layer effects to the ponies them selves.
Such as a brown (grabbed from the mountain) inner shadow on multiply and VERY slight outer shadow same color settings with your light source coming from the lens flare behind Spike. I input bout 110 degrees.
To add more depth I even went in and added an inner bevel to the masked pony layer with an interesting gloss contour of white input of 70% and output of 90% and a mid with input around 60 and output of 50; also found that oddly 39 degree altitude did something much different than 40 degrees when I had the light source coming from 110 degrees.
Overall giving off a cool silhouetted sunrise effect to the ponies and highlighting the coolest character EVER! (Spike ;p) Really made it POP and decreased this WAY TOO BRIGHT problem.
So there you have it folks. xp
Finished image: http://i.imgur.com/jUGZiSD.jpg
Easy post production things to do to really make your image shi-i-i-iiiiiiiiine.
Besides this small tutorial I really like how you stylized their faces. Really cute.
Really captured their personalities well, too.