Simple, but not bad. The only real problem I see is with the layout. You can't see all planet buttons unless you zoom out enough, and once you reach ten planets, you can never see all of them at once, despite there being empty space above and below. You should always be able to see all buttons as long as the screen can actually fit them.
Likewise, the multiplication and exponent numbers on top get too wide to be displayed.
It would also be nice if the multiple-buy options would buy as many as possible if you can't buy all of them at once. Having to click those to adjust for that all the time got annoying enough that I just use an auto-clicker for increasing Hz.