There's a huge variety of styles that are very effective without being time consuming, and are very under-utilized in games. Of course it does take some time and skill to make everything work together.

Regarding the current style (which of course you should stick to to finish the game, but might consider this in the future), I personally dislike the "inverted" color scheme - it is often (over)used to evoke a sense of shock, other-worldliness, or outright inversion (light world/dark world), but to many people it only evokes the thought that the artist simply used a single photoshop filter to try to make it look interesting.