In response to your review request:
I think on this one you were working against yourself in a lot of ways with the color choices. You've set the seen at night, but you're afraid of embracing that with the colors and values, really play into the night scene. That light/mid gray of the buildings should be black, or at least the darkest areas of the piece. The lights in the windows should push the contrast and inform the shape of the city, and should not fill every single window in a building. Look up references of city skylines at night, and use them; some buildings will catch the light of big light fixtures and reflect that light so if there's a big neon sign the buildings next to it should be that color too. There is also a phenomenon called city glow where the sky around a city is a perpetual hazy yellow color, so that would gradate up into the darker sky. I'd recommend gradating from yellow to maroon to violet to blue-violet.
You can also add depth to the background with some more washed out buildings being cut off by the closer buildings, and then further obscured by city glow.
Also some smaller but closer buildings in front, or some ships on a dock will also help to sell the concept of this being a city on a lake, or port, and look a little better as you transition to the bottom of the buildings to the top of the water.
At night water tends to look black more than blue, but it is dark blue and does match your current BG, so it works, but having the buildings perfectly reflected wouldn't happen. They should be more distorted, and diffuse to be wider as they go out, and the yellow of the lights would catch the tops of little waves that are white.
The character lit as though he were standing in daylight, again use references for skin tones, or establish that the surrounding area has a bright lightsource, something as simple as lamps in the background, but that would require pushing the ground he's standing on back, or extending the width a bit to manage. Beyond that look up how skin is affected by low light, or if you were to add a lightsource how it is effected by the color.
His legs look pretty awkward, I would recommend turning the foot on our left in more, even just mirroring the outline should work, right now he's pretty duck footed. The pant legs on both legs would probably look better if the curves were flipped to cover over the shoes rather than bend up; right now both feet look to be bending forward in front of the legs themselves. There also looks to be a kink, mid-shin on that left leg, so watch out for that.
Looking at the right foot, it's out of line with where you're denoting the knee on that leg to be, I would recommend shifting it so the knee matches the foot more, right now it looks like he's turning the right leg into himself, which disagrees with his chest and waist.
The folds on the pant legs are a bit dramatic, I can see they're informed by reference, but it looks like the shading got lost a bit in the translation, the way the highlights are catching agrees with the coat, but then there's a shadow on the edge of them where the light is being caught.
The sword is also really bright, if it's supposed to glow, make it a light source and clearly denote that, if not, make it so the only bright spots are it catching light.
As for the expression, I'm assuming he's winking and doing a cat face at whoever he's pointing the gun at, which given the information we have is the only real assumption here. His eyeline is not at the viewer like the gun is so it's got a bit of disconnect.
Another general composition note is put something in the foreground. A crate, the shoulder of his target, really anything that will sell the scene a bit better. It looks more natural and also will serve to frame your character and draw the viewer's eye to them.
That was pretty big wall of text, so let me say it's great that you're doing full compositions, and taking on more challenging poses and concepts. There's a lot going on in this image, drawing a character, skyline, ocean, all at night, is ambitious, there are a lot of great references that are easy to find of scenes, they're going to help you a lot.
My main advice would be get more comfortable with working with bigger shapes. The cityscape background can be accomplished with a few well placed large brushstrokes and then gone in with a smaller yellow brush to dot in the windows and a more transparent brush to get some highlights and shaping in. You don't need to go straight in for linework or shape tools, especially for BG's. Same with the water, going in with a big chunky brush and implying the lights and waves would be quicker and probably look more naturalistic.
Keep drawing, keep working on anatomy, Posemaniacs and line-of-action are both great websites for anatomy. Use references, and think more in terms of shape than line, when it would be applicable.
