First off, this piece has a very good color harmony and very bright colors. It shows that the author clearly has a good understanding of color theory. He uses darker colors for the shades and analog colors for the lights (See the tablecloth, it's light green, shaded with darker green and highlighted with yellow).
The characters are all taking carefree attitudes. But, do they fit the picture? If you animate it, what is each pony doing?
Soarin' is jumping at the cake, hungry or perhaps just wanting some candy. Spitfire is giving him a friendly glance. Rainbow Dash seems to have noticed his intentions. Pinkie Pie is watching some candies directly in front of her, smiling.
Fluttershy has the most collected look, as she has closed her eyes and appears to be singing. Only Fluttershy can sing just before the feast. The curls of her hair are very nicely done.
Applejack, on the other hand, seems to have taken Pinkie Pie's place while she eats: she is breaking the fourth wall, looking directly at the viewer with a defiant yet friendly attitude. The just married couple are at the background, cuddling.
Rarity has no interest on the sweets, instead taking a glance at her hair, maybe checking if it still looks fabulous. The royal sisters for their part, are looking at the entire scene. However, Luna is unable to look at the table, since both Celestia and her mane are blocking her visual field.
Twilight Sparkle is the most rigid of all the ponies, since she is only looking at the front.
The setting also has a lot of detail. With a roman style, the building has several columns with all sorts of colorful motifs on them, like vines and flowers or pony silhouettes. The tiles are very shiny, since they have reflections. And at the background, you can see a lot of stars on the dusk sky.
There are, as in any artwork piece, fields of improvement. The cake and the pie on the table are assymetrical. The shadows are just pencil strokes, and really aren't in the direction of a light source. The sky could use a smoother transition or more subdued colors, since it seems there is fire on the horizon. The shapes look a bit sketchy: there are a lot of definition lines on it. (e. g. Fluttershy's eyes) The floor's perspective is off (a bit more tilted to the front than it should be).
Overall, it is a very detailed and colorful piece.
pinkie's hair is sooo great I never seen her hair like that before you didn't only put detail into the picture but you were able to show the personalities of each ponies thats what good MLP art is not just making cute ponies but showing how there different.