Ok, this is what I noticed while looking at the map.
-6 minerals isn't enough. This will make strategies like a 9 pool for Zerg difficult as the timing will be screwed up. It'll also slow down a Terran considerably as SCVs already gather slower than other peons. 8 to 10 would be good for the main bases.
The two bases nearer the middle need to be altered. A floating Barracks or Engineering Bay and a Tank or two will pwn the players economy. You need to pull their resources and command building away from the edge.
-I really like the routes around the map, similar to Bifrost. However, the one bridge in the middle could become problematic. I think you should make the land outside of the bridges unbuildable. That way a Terran player can't camp their Tanks and Missile Turrets without having to think about disturbing whoever is mining at the middle expansion (assuming it's them or an ally).
-The base at 11 is a bit cheap. The resources are moer easily reachable because they aren't in an odd alignment like the other bases. The command building is one matrix square firther away than it should be, so if a Terran lifts their Command Center and moves it over they'll have an economic advantage once they make up for a late SCV.
-I would work towards giving each base a more easily defined natural expansion. I can Zerg having a lot of trouble on this map as they can't build Sunken Colonies in many chokepoints, the openings to bases are too large. Zerg will also have trouble if they lack an expansion with gas. Zerg needs gas to fight M&M Terrans early in the game. It will be impossible for a Zerg to fight against SK Terran on this map if a Terran enemy manages to secure enough gas. 3 Fac Tank will also be very bad for Zerg.
-In the bases between the two edge bases on each side, the mienrls should be curved to complement resource mining. Also, I think you should have the Vespene Geyser nearer the minerals there. If someone can make a successful drop, they deserve to be able to do more damage to peons without having to run around the base hoping reinforcements don't come in quickly. It will also make players feel a little safer not having the Geyser so easily exposed to anyone who makes it up the ramp. A Terran can fly an early Command Center to these cliff protected bases. I would put an 8 mineral patch right in the middle so it's impossible to land a Command Center without first dropping a peon there and mining the small resource chunk with it.
-10, 11, and 5 need to have a different plan to the mineral placement. To combat ranged units dropped behind the mienral lines, the defending player also needs ranged units. These units will get stumbled up in the mining peons if they misclick. This is mostly an advantage for Terran as Marine drops are inexpensive. That also makes Revear drops impossible. Reavers must be dropped in the mineral line which makes it mroe likely the Reaver will be killed before it can deal sufficient damage for the effort of dropping it there. Have paths around both sides of the minerals that units can go through. Alternatively, have one way through and have a break in the middle of the mineral line.
-The main bases are a bit big, so restructuring the terrain to accomodate some of these suggestions should result in more normal sized bases which is good.
-There are expansions on the cliffs southwest and northeast of the middle main bases respectively. I think those should be on low terrain. It will make players work a little bit more to defend it. It will also make it so a Terran player can't defend his team's half of the map with a few cliffed Tanks and Missile Turrets.
-Just south of the middle of the map is a doodad that doesn't belong between the cliff and ground. It doesn't fit there. With the current map pattern, you won't really be able to blend it in. Also, it'll cause vision problems if a unit steps near it, they'll lose sight of the cliff they're supposed to be on, and units below the cliff can see and attack there when they shouldn't be able to.
-One last thing is gas placement. It's faster to mine gas from the north and west then the east and south. Choose which of the two possibilities you want to use for the map and stick to it, otherwise you'll have some balance issues with gas.
This explains the gas issue better.
--------------------------------------------------
You have a good design idea. It just needs to be modified to accomodate a wider array of strategies. The resource related problems are the biggest problems but those can be dealth with with relative ease. This map is also incredibly friendly with Terran and difficult for Protoss. I can't see how a Zerg could play well on this against Terran or even a decent Protoss. Changes I suggested should alleviate these issues.
It's a good map, it just needs some polishing. There's a lot of things that need to be changed, but none of them are major.
If there's any changes I suggested that think would conflict with how you wanted the map to feel, disregard them. Make only the changes you feel comfortable with, but everything I suggested has a degree of validity. In the end, it's your map. Do whatever changes you feel would be beneficial.
If there are any suggestions you don't understand, I can take screenshots of changes, but I'd need an unprotected copy of the map. If you don't want to send me one, then I'll try to clarifiy anything you don't understand with drawings and more specific explanations. Also, I haven't spell checked so I may have made some bad typos.
It's a reasonable map, I can see some good 3v3s being played on it with a few changes.
But it works fine and accomplishes the task. You have a split of 4 mienrals on each side which is good as it won't disrupt worker splitting. My only concern is that the peons on the right side are more vulnerable to attacks.
