It'll really only be good for side view games.
And even though penguins are dark, you really should add in more there in the black spots. I can kind of almost see something, or that's a scratch on my monitor - can't tell. But it looks really like a blog in a recognizable shape.
Even things meant to be black, aren't really black in spriting. A black coat will have shades of blue, purple, and some gray in it - at least if they're good they really won't need any more than a shade or maybe two of gray (most good looking sprites use a blueish/purple like color as highlights and tones instead of just lighter shades of gray).
Try going over it with more colors to see what I mean.