they're right... you need to place in some sort of gamma to allow users to set the darkness to a comfortable level - i'm surprised an artist who can achieve this level of graphics didn't tell the programmers this already.
You need to hue the whole screen, because if you want to add true atmospherics then you'll need to make sure that the lights actually ditact the lightmaps produced onto the entire area which should be alot stronger than they are.
Remember graphics aren't everything, i personally never enjoyed diablo all that much - its not because the graphics were poor, i found them quite pleasent. No its because the actual gameplay didn't appeal to me.
This is only my opinion but i'm unsure on how you can improve a game which genre wasn't entirely fantastic to begin with. Thought i'd have to wait to play a demo version to see if i enjoy this any better.
Now i could be wrong, and i hope i am - but this appears to be FULL 2D ... now i'm unsure as to what kind of speed and space this game will take up, and how graphics card friendly it'll be.
If you've never seen TheSims, althought yes it is technically a completely different game - i think you should check it out and take note on how they've achieved thier isometric 2D look with real 3D graphics
then if you want something to really boast about you can include in stencil|projection shadows - full lighting effects - interpoled skeletal animation - smaller file sizes and rendering sizes.
Simply by making things Textured 3D, and if like Diablo you're having a SET veiw - then it is quite easi to render and texture the render and alphamapped textures onto simple block which can be affected by light and even have damage textures or be destroyed like crumble into peices which would REALLY give you an edge over diablo
Anata aru kowagaru no watashi! 
