Ahhh, at last I feel like I can make some sort of note when concerning graphic design. My GFX knowledge is rather limited, but I think that Gliscor really hit the nail on the head with that one. I'd like to expand on that further.
And keep in mind this is all my opinion, based off of the knowledge I've gotten about basic art design over the last however long.
The amount of color is not necessarily the problem; it's the copious and erratic amount you have used. The biggest thing to keep in mind with art is to get a solid composition down. If you are to use a vast amount of colors, there needs to be some harmony to balance out the contrasting chaos of the mess of colors, in such a way it does not end up contrasting the thing itself.
For starters, I'd like to take a moment to note the Espeon sprite avatar you made. Sprites, as you may or may not have known, are 'hard' pixel objects, typically based off of a very small color pallet of 32 or less colors within the actual sprite. (This is why GIF is the most generally used format when dealing with sprites, besides PNG (for its losslessness).
However, although I am not sure which program you're using, one thing seems sure to me... you have brush and opacity settings available. Those tools are typically for rastor images, such as painting and touchup. They are known mainly (unless I'm wrong, then someone correct me) as anti-alias tools or feather tools, as they typically have a much softer edge than Pencil tool. Pencil tool, on the contrary, is an alias tool; it means that the edges are very exact and the like.
Combining anti-alias and alias tools, unless you know EXACTLY what you are doing (say, for the exact purpose of making that note of contrast), should generally be avoided and generally speaking, is unpleasing to the eye because the two don't match so well. So I'd generally stay away from that much...
Next up is the chaotic scribbling itself. Well, that's what it looks like to me, at any rate; it looks like you used many many different colors to overlay one another in some uncalculated manner...and it's...well, it's generally not such a great idea, IMHO. It makes the entire piece look rushed and unfinished, especially since there is no border of the sorts. The colors you've chosen aren't necessarily bad, but they do NOT overlap so nicely. The prime example of this is that really large image with the colors and nothing else on it but the wording. Specificially, the left side has this kinda ugly brown-green color going on. Granted, color is a matter of opinion with likes and dislikes, but it sticks out horribly against all those other beautiful colors you smashed into that image.
Another few things of note were some other unpleasant contrasts and attempts at harmony; the Team Darkness stock looks VERY unsettled in general. I'm also not sure what you did to the stock itself, yet it doesn't quite look right. If you were attempting to bring the 'opacity' of the image down without actually editing the layer by smudging over it with your kinda chaotic painting scheme...I dunno. It just generally does not fit for me. The large whitespots for 'Team Darkness' also aren't quite doing it for me...shouldn't a deep purple or some other sort of cool color have been used instead of the white to give a better feel of the word 'Darkness' BESIDES Darkrai? ...and on some of the later ones, I noticed two brush sizes. Just two- one rather large one and then a tiny one. I'm not sure how to say it, but that contrast is really distracting to someone's eye on the image. If you wish to bring some nice balance to the piece, you have to have about 5-9 differently sized brushstrokes to bring the contrast down to a suitable and more pleasing point in the artwork.
As for the last one, the Sonic one, there is actually TOO much harmony and not enough contrast. The text and the stock do not very well go with the background, seeing as they're nearly of the same hue. A green-blue-violet mix in the background, done in a radial direction around Sonic, would have been FAR better a choice. (And by radial, I mean using Sonic as the focal point and drawing lines that point to the middle-most part of the image to bring the attention in on him, which is what one wants most of the time in an art piece- to focus on the subject). The text itself could have been blue-outlined yellow, or blue-outlined red. The point is, the Sonic one just doesn't have enough 'pop' to it; they both need to have some more distinguishment in order to give the impression of Sonic actually being the 'fastest thing alive' and not Shadow. :B
Before I go on, I suggest searching DA for 'composition' entries. I'm sure that there are some basic composition entries that one could read or follow a tutorial for.
Composition of an image, as well as using a balance of harmony and contrast within an image, is one of the harder parts about being an artist. I myself struggle with composition all the time. It's a matter of practice and reminding yourself to keep those elements in check.
But, I shall say this- I'm unsure if you took the opacity of the colors down or not, but the last one looked FAR less sloppy. If you fade colors into one another more, I think maybe you can get away with the scribbly thing. ;D
...yeah like I said all my opinion. :B So it's not God's word or anything like that! You're welcome to disagree with me and tear me apart for my suggestions and beliefs. Or not. You could do the opposite. Either way, I will stand firm on my beliefs.
