Ideally you want more things having their own pipe run back to the equipment pad, and 2" pipe through out (except larger for the spa as shown). Pipe is cheap, so it doesn't make that much sense to plumb a pool this way. That said, this kind of plumbing is fairly common, and it does work (if balanced correctly). It just that given the minimal extra costs it is clearly better to do it a more modern way.
You appear to have dual main drains connected to the left hand skimmer? If that is correct, that is more than worth changing. It is a huge advantage to have the main drain plumbed separately back to the equipment pad.
On the returns, it is very difficult to balance the returns when they are plumbed that way. It can be done that way, but usually they end up unbalanced. Since the return pipe already goes 3/4 of the way around, it seems worth running it the full way around into a loop as vinper suggested. That will automatically balance the returns with little effort and minimal additional cost. If looped, it should be 2" all the way around.
Using 1.5" in the line to the far returns as drawn isn't a great idea, though it does have some justification. The additional water velocity in the pipe doesn't help anything. You get your jet velocity by controlling the opening size on the return eyeball. The way in which it makes sense is that as you pass each return, the amount of water going through the pipe goes down, so you don't need as large a pipe. With careful choice of return eyeballs (with the ones closer to the pump having smaller openings) the system as drawn could work out. But I would never do mine that way.
The skimmers will also be unbalanced. Ideally they should each have their own run to the equipment pad and each have their own valve at the pad.