I want some opinion, I know this is going to sound like alot of the others.
Same crap diffrent person ==> This is my first melee map, just to note.
Twilight, 2 Player, 64x64
For your first map, it looks nice. I like the layout. However, you should make sure that the minerals are always balanced, and you seem to have gone a little heavy on them. Also, vary up your terrain a bit more, make it purty.
True. The layout looks fine, so I'd suggest a couple aesthetic things: vary the terrain--throw in some crushed rock/mud/whatever, maybe even some Basilica. Also, move some of those minerals. It looks artificial when they're in straight lines. Just stagger them a bit and you'll be there. And there do seem to be an awful lot of them.
[sub]Layout is NOT fine. Blues ramp leads into an exclosed area whereas reds opens up to the open. Blues rank can only be attack from one side, reds can be from any direction. The minerals need to be even on both sides. Fix those and you have a boring, ugly, and balanced map.[/sub]
This is a hard setup to attempt, you have to know melee pretty well to try things that change game balance (i find myself wanting to say this to many people recently). If you try another map, stick to something alittle more simple (2 or 4 players, symmetrical, etc)
You should spend more time when you make a map, this looks like it took 20 minutes max. Do what valug says if you want to keep up with the map.