Hi, loving the machine! I'm a former art director, so maybe i can help you with a couple tips on how to get the most out of your graphics.
The text being brownish, with a black outline, and tight kerning (the space between the letters), is leading to a very muddy look. Contrast is your friend in these kinds of applications where you want things to be bold. So, be sure to pick colors that stand out from each other. Don't kern too tight because the contrast between the text and the background is also important. If you do need tight kerning, be sure to make up for it by using high contrast colors. A trick to make graphics like this pop is often using what I call color shells. Your text has a fill color, and an outline color, it can also have a shell color which is outside the outline. Typically I use white or a very pale color as you need to keep high contrast with the outline. This can make text with a dark stroke on a dark background POP. you can make it pop even more by adding a subtle drop shadow. Look at old arcade graphics and you will see loads of variation on these simple techniques.
The background is kind of boring with just a gradient, and a kind of calming blue. The idea of Monkey Ninja just screams bounce off the walls action, but the background is not carrying it through. I suggest something in the red orange and yellow area as the basic palette, as those are action colors that go with your theme. You don't have to use them in their full color strength (like ketchup and mustard), they can be used as tints or what-have-you to make a subtler feel. The background does not want to overpower the text.
As for background graphics, you don't want a lot of detail, but you do want the feeling of an environment. This can be very simple using things like silhouettes, or even layers of them. Some outlines of stylized Japanese buildings, trees, etc. could be cool for a "situational environment", you could also make a conceptual environment, using silhouettes or outlines of ninja weapons, or ninjas doing karate moves. Less is still more in this area though. a few well placed images with the right colors can make a huge difference. Saumurai Jack is a great example of both color palette, and making simple graphics work hard for you. Some inspiration:
http://tinyurl.com/bvsaa7lAs for the monkeys, I like them. One note to consider is that an outline around them can also make them pop if needed. It can also denote directional action if used in other ways. You could add some speed lines behind them for one.
Anyhow, I hope this helps. Best of luck completing your cab. Looks stellar so far!
