Wow. This has to be the first B&W wallpaper I've ever liked. It's simple yet elegant. The reflections are a very nice touch and just add to the quality. It's also cool because you've got the most favorite expressions of the Joker. It's hard to find any mistakes about this one. Yet it's not a mistake, but the woodlike texture for the BG... I'm not sure, but there is something about it that I don't like... It goes well with the whole wallpaper, but I'm not sure... Somehow it seems out of place... Maybe try a different texture?
IMO, for added awesome, you should add a touch of colour. Even if it's just giving the colour back to his lips in the middle picture. Try something subtle, if you can. Good work though. As Jugg said, elegent, simple, effective.
You would. Anyways, the addition of the red makes to look better IMO. The bit of color adds to the image as a whole. It makes it stand out more.