Looks neat, I would love to see what comes out of this gamedev project! I'm also working on a game, but mine's not ambitious, but hyper-indie and low-res. ;)
Haha, the similar color to my castle in the sky is actually a coincidence, because the color scheme on this actually came from cave story.
The robot turrets also weren't meant to resemble the ones from castle in the sky. Originally, they were supposed to have 2 rounded sticking out gun barrels, but I had to change it due to readability and shading issues.
Funnily enough, his last piece was a Castle in the Sky fanart, no doubt he was at least unconsciously inspired.
But yes, this is very nice, I especially like the background tiles.
Liking the dark background a lot. I do think that the character should maybe have a bit more of a dynamic pose though, atm he looks a bit rigid. Very nice.
Reminds me of Castle in the Sky, with the robot turrets and general colours scheme.
Thanks for the crits. I've lightened and added some shading to the player:
https://dl.dropboxusercontent.com/u/12694594/shooter%20mockup.png
It's quite tricky to keep the details of the sprite seperate from eachother while at the same time being readable against the background. 
I think the contrast needs to be worked on a bit, right now the monsters and player fade into the background too much. The tiles a really pretty though.
I like the terrain a lot, although I find myself wanting more contrast in the foreground. Also the style of the player does not match the style of the rest of the image. I think he deserves a little more attention.
Really nice pastel and muted tones in this