The map's layout is interesting and well detailed and although the arrangement of the starting positions seems a bit impractical for 3 vs 3 (north vs south), 2 vs 2 vs 2 actually might work quite well on this map.

It seems that the visible area of the map (the blue rectangle) is slightly off since some of the details (including most of a tiberium field) are outside of the blue rectangle, so you're best off fixing that by changing the Width of the visible area from 103 to 107 or so.

The distance from the starting positions to the tiberium fields seems to be a bit unequal, but I suppose that individual players should be able to properly compensate for this themselves with a slight amount of base-crawling.
This brings me to the next issue however; although the trees you placed are a nice detail, there are too many of them near the starting location and they'll get in the way of base construction a lot. So try reducing the trees in the areas that were players will be building their structures.

The bridges are quite long and since these are the only passages to get from one island to another it might be more practical (and also look better, because of their length) if you'd make them 3 cells wide instead of 2. To make bridges wider you'll need to copy/paste a part of the bridge and overlap the bridge endings with the tiles near the end of the Bridges tile set.

Here is the improvement of the map.
And to the starting positions: it was a crazy idea from me to make a 2 vs 2 vs 2.
I made the bridges 4 cells wide instead of three.

That's a good improvement. The 2 left bridges now have some errors where they connect to the cliffs though and the far left one is also missing a small part of its shadow (it seems you forgot to include these cells when you copied the bridge), which makes the border of the shadow that's left look like a sharp line.

Okay, now I improved the map.
Seems like I forgot to make the shadows there trough copy and paste.

Well done, it looks good now

Very nice. Keep up the good work

(We staff should really make megamaps faster so we could post these gems to ModDB =P )

And I'm guessing that with we you mean me?