Hi there, this is not a critique. Just MHO.
This tree has very nice shape. I like it. Overall, in my mind, the skeleton for a future bonsai has been set up. The leader should be thicken a little to be in proportion with the main trunk. Likewise branches should be developed in accordance, and foliage pads need to be defined.
I could not tell if it is a real rock or a cement block. The roots on the rock, if not developed much more substantially will keep this tree looks immature.
I would cover the rock completely using moss or coconut coir mulch to stimulate more roots over it. Also I would be mindful with cross roots on the rock.
Just my
Best regards.