First thing that comes to mind is that Red and Blue's main gas look slower. Try moving them to the top of your SL. Purplers minerals look a little slower as well, but that may just be me. Teal has less cliff behind him, either match the other players to him, or match him to the others.
I think Terran have too many advantages on this map... at least against Zerg (probably more so against Protoss, since Zerg can always go Mutalisks). For Zerg it's going to be really annoying trying to defend a nat with two chokes, while the Terran ineviatbly goes tanks droping on his main and natural. That's just what I think will happen... I'm theory crafting here.
If I were you, I would close off the parts of the nat closest to 6 for Teal And Purple, close off the parts of the nat closest to 12 for Red and Blue and then open up the top of 6, and the bottem of 12 to make them accessible.
Putting a cliff right behind the main minerals still scares me, especially since the dropship has a completly clear path to it if the players are on the same side.
If this is a 2 vs 2 map then I have no idea... I'm assuming it isn't.
Cheers,
Okay, I updated it, So it isnt that unfair for all of them.
I gave it some more look, Gave them all an equal ammount of mineral/gas income, And disabled the tank drop behind there minerals.