I'm surprised that none of the entries really look like an existing Eeveelution. I was expecting most of the sprites to be in a stock quadruped pose, but these are all pretty creative. While Necteon is probably the most original, the pose and design prevent it from really being recognized as an evolution of Eevee, and the colors are a bit too pale. On the plus side, the line art and shading are near-perfect, in general.
Minareon has a similar issue, though it's more about the shading. The highlight shades just kind of blend in with the main color, making the shading look a little too soft. More importantly, there's very little black in the outline, making it look... Indistinct, I suppose. What I do like is the front legs, which are shaped/positioned exactly how this type of burrowing creature's would be. The claws could be a little sharper, though.
Another sprite lacking black in the outline is Wyvereon, which is a problem with the bright green used on the outline in some places. Unfortunately, the one place with a good deal of black is the whiskers, which makes them stand out and look more solid than the rest of the sprite. The biggest issue is probably the shading, specifically the amount of contrast. The bright green used to shade is barely darker than the bright green used as a base color, resulting in a sprite that's a little hard to look at. That being said, I voted for this entry because the design itself is interesting, and it's in a dynamic pose.
Inviseon is an interesting concept in that it literally resembles a Pokemon-style ghost, kind of like Gastly, but the execution isn't fantastic. The biggest problem is... Well, it's big. While the canvas size is 96x96, you don't have to use it all to properly convey your idea. It's also a bit lacking in the style department; if the artist who drew this is interested in spriting and would like to continue, I recommend getting a little more hands-on time with official Pokemon sprites, to learn how they're designed. I've written a tutorial on playing around with Pokemon sprites to create original designs, so that would be a good place to start.
Like a few of the other entries, Wispeon's contrast is a bit low, and it could benefit from deeper shading. Its design is interesting, but the one glaring issue is that it's not very Eevee-like. If you were to tell someone it's a Ghost-type Eevee, they'd say, "Oh, okay", but if you just showed it to them, they'd say, "That's one creepy-lookin' ghost thing". It's in an interesting pose, however, and the overall design isn't bad.
I'm not sure what to think about Lepideon. The choice of colors work well together, and the shading is fine, but I'm finding it hard to like the overall design. It doesn't really look much like a bug, and while I'm happy to see an entry with a thing-around-the-neck similar to the original Eeveelutions, I can't really tell what that thing is supposed to resemble. I also can't help but feel that the head is a little too big and the legs are a little too long for the size of the body, especially considering that bugs typically have smaller heads and keep low to the ground. Despite all that, of all the entries this one looks the most like an evolution of Eevee.
Finally, we come to Ghasteon, probably the best-drawn and most consistent with the Pokemon style here. The design and color choices are great, though the lack of shading makes it look a little flat in places (most notably the left-front leg). Exacerbating this is the bandages, which look flat and drawn-on rather than actually being there pretty much everywhere but the head. Speaking of the head, we come to the reason that I didn't vote for this entry; between the elongated snout, ears that point straight up, and the mane and tail made of smokey gray ghosty stuff, it looks like a pony. I know that the snout is only shaped like that so that the bandages could wrap around the way they do, and that the ears would have looked like perfectly normal Eevee-esque ears otherwise, but I just can't stop seeing it; that's an undead pony. That's the younger brother of Nightsteed from Neopets.