Is it the scale that's the problem? Some plain blocks don't translate as well from a small size to a large one. You could try putting small pieces on top to break up the blocks - see if that's it. If so, some excellent suggestions about applique, fancy quilting, threads, etc, already given would break up large expanses of one color.
I find that I usually have to systematically model one change after another until I find the one that transforms everything. Sometimes, it's just removing or substituting a color. Given that your top is sewn together, perhaps there is an addition that will turn it into something you love.
hugs,
Charlotte