Impressive connotes the ability to impress the mind, so that you’re in awe and respect for them.
A god which creates out of nothing, does show the ability to impress your mind as you would be in awe. This is because it shows the omnipotence the god with holds. This is because it would take such a powerful source to create something with no material so magnificent, only a very powerful person would able to do such a thing. Therefore this shows a god which is impressive.
However having a god that creates out of nothing is not all that impressive. If you create everything then you create the defaults with it, so when you create a world, you would have placed all of the negative points there as well, such as evil. Evil destroys people and therefore how can that be impressive? Would you want to live in a world full of evil? Where no-ones’ life is safe, and nothing is ever certain, just a life of constant pain. Therefore this does not impress our minds as it shows this god to be just omnipotent but not omnibenevolent which would be more important to many people as they want a caring a loving god and placing evil there doesn’t display this as who would want to create such a thing?!
A god however who creates from existing material is not impressive either, as it doesn’t show their ability as it would creating out of nothing, it demonstrates no power. Anyone can create from something which is already there like play-dough anyone can sculpture it, into what they’d like it to be the shape of.