@goosemonger:  I suspect that the odd perspective is because it's for this contest.  Correct me if I'm wrong, Huge.

Now for the art:
-The art looks pretty nice; I especially like the grass and stone tiles.  You may want to increase contrast, or even add more detail, on some of the brick tiles, especially the front of the barbershop.

-Speaking of the barbershop, the perspective on that is off, if it is intended to have a gabled roof.  If it's intended to have a different roof, feel free to ignore this next comment.

To draw a roof in perspective, especially in a funky one like this, several steps are necessary.  I started with a simple box onto which I plan to put the roof.  I then marked the center of the gable face and drew a line up to where the ridge should go.  I then connected that to the box, removed the guidelines, copied the gable to the other side, and cleaned up.  The next step would be to divide it into tiles, texture it, and so on.  (Please note: when I drew this, I was not thinking about tiling.  If it were intended to be tiled, I would have used much cleaner dimensions.)

-You may want to consider removing the black lines at the base of the barbershop and around the door.  They detract from the image a bit.  The ground line could be easily removed or even just replaced with the interior detail color from that face of the building.

-The buildings seem like they're floating.  I don't know how you're doing on tile count, but you may want to consider adding shadow tiles.  They might help in holding the buildings down.

Overall, this is a pretty nice tileset.  You've done a very good job at getting a lot of details into 40 tiles, which is commendable.  Good luck in the contest!

Just a thought: dithering doesn't usually work too well on metal.  That and the colors don't define the form very well.  It would help if you differentiated between the darkness of the colors more; there's plenty of hue differentiation (were you trying for 3 lightsources or something?), but the mech seems really flat from lack of value differences.  The internal black lines don't help much either.  That's more than one thought.  Whatever.  It's 1:00 in the morning.  Good luck with the mech; that's some really complex lineart.

I forget who did the lineart, but I think the other mech is by Zach.  There's some pretty cool stuff in this thread; I always love seeing what people do in collaborative environments like this.

Hey Vicious Zen; welcome to the boards.  Regarding the sprite tutorials, there's a wealth of knowledge in this thread.  Check out st0ven's site (spriteart.com) especially; it's got a bunch of useful tutorials for beginners.

On to the sprite:

-I disagree with CAG regarding the color choice; there's nothing wrong with "normal" colors.  That and there's nothing "normal" about green hair :-P  Not that it's a bad thing, just not normal.
-The headphone cord (if that's what the white line across the torso is) needs more contrast.  Consider making it white, or at least almost-white.
-The pants shadow color could stand to be darker; a bit more contrast there and on the shirt would help define the form a bit better.
-The hair is very flat at the moment; in fact the whole head is rather flat.  Again, contrast will help you here, but you will need to add some shading to the hair.
-The outlines look ok, but some selective outlining might be a good idea; the outlines look a bit jagged in places, notable the front of the pants.

Overall, it's a good start, but the sprite does need some work.  Good luck with this.