Two sling spots aimed at the center of the playfield would brighten it up sufficiently if it bothered you.
I think it looks great the way it is.
Quoted from mpnox:
Yeah I kinda reacted the same way, looks very empty right in the middle but it's not too bad actually.
Of course Pin Stadiums would light this baby up like a christmas tree.
EDIT: Took a picture with glass off and turned down the ambient light.