The mains are rather small to encourage expansion rather than turtling, as the mains + nats are VERY easily defended. It also discourages rushing to air units to hop the short gap.
Except this isn't really what SC was made to be.
I agree with all the points ImagoDeo made, but I will also add these
1. The Rush Distance is wayy too long. Compared to air distance, it is ridiculous. This makes rushing much less advantageous than making air units.
2. There're choke areas that are too tight. This makes Zerglings/Zealots/Melee units weak. It actually isn't that easy to defend if you're being rushed by marines, and all you have are zealots that can't do their job well due to the tightness.
3. A question would be whether you've played as a turtler before. If, let's say, I had a layer of bunker/spine crawlers/cannons along that L shaped ledge leading to my base, all melee units trying to fight in that area will be completely useless cause it's just so clogged up!
4. Brood Lord/Banshee/Void Ray + range Massacre!!
5. Proxy Reapers Possible. I can build a barrack, and land it at the side where rocks were used to block the path. All your base are belong to the Reaper-men. (OP due to the hugely comparable rush distance for all other units)
6. Strangely placed nats (minerals blocking) will make melee units cry.
7. Number 1, 4, and 5 are the same problems as my map too.. so you're not alone D:
What I do like is the beautiful texture terraining. I can finally see how textures can be a beautiful thing
I think the concept of pushing people to expo isn't all that of a bad idea. But this isn't the way to execute it.. I think if the main can't be well protected, but the expos can, then people will try to expo more. Or if the rush distance between mains are very short, but it is longer to expos, then I think it'll drive people to expo. However, will this be an imbalance in it of itself? I don't know.
EDIT: One more thing.. too many xel'naga towers.. ignoring the one in the freaking base.. if I just spread my workers out, there'd be no way I can miss a rush coming. I'm not too sure if this is a good thing.
None.