Well done, you can do //hsphere 1,98 7(ish).
Needs more detail, it just looks like a couple of //hsphere commands, which doesn't take much skill to do.
Add more detail, a variety of shapes, some ores on the inside, another one of the smaller islands leading to mid, having 3 of them just looks weird. Add some anvils, enchanting tables, chests in not obvious places, maybe a couple of hidden ones you have to break blocks to get to. But the thing it needs most of all is detail, it needs a variety of shapes. Rocks are barely ever spheres naturally, go do some research, Google rocks, go outside and look at some rocks, start to figure out its shapes, then recreate it in minecraft. I'm pretty sure rocks aren't a mixture of stone and stone brick naturally either, maybe try out some different blocks and experiment.
But overall, not enough detail for sure.