I absolutely LOVE this piece. It's truly a work of art.
First off, the color choice is perfect. The shades of pink, yellow, and blue are accurate and go well together. They're kind of Easter egg colors, bright and cheerful and very fitting for Pinkie. The background colors go well with all of the other colors. Brown and green is quite the contrast to Pinkie's bright colors, and it's very easy to look at because of the shades you chose. I also like the way the yellow is used on top of the green to the left of Pinkie Pie. It brings light to the piece, indicates the light source, and is just one of those things that completely changes it for the better.
Now, the style in which you drew the lines is fairly simple, a little bit sketchy, nothing new. However, the way this was colored is very, well, unique. It's kind of fun to look at. The shape of the brush used is clearly square or rectangular. There are many ways this style of coloring could have gone wrong and looked much worse, but you did very well. I like how there are spots of white on Pinkie's mane and tail. Fantastic. As pointed out in his comment, "The colouration gives it a lot of movement which fits Pinkie..." I couldn't agree more.
The general style of this piece is interesting. Very well done.
I'm giving you fives on everything but originality, simply because there are tons of people who draw Pinkie Pie. Normally I would give you a 3 for originality, but your style is very different, very original, so I'm giving you a 4.
Yes and going to someone's artwork to tell them they dislike the character the person drew is very helpful. That is like going to a bake shop and yelling, "I hate to say this but I find cake and pastries to be fattening and disgusting", and then leaving. Also, if one hates to say something they don't really have to say it, now do they? :3