This was a huge improvement over 5.5 IMO. Couple things I noticed...
1v1 Kulas Ravine TvP
1. I built one of my expansions in a base where both ends were blocked by boulders. The AI was too dumb to destroy the obstructions and just stood there. When I approached on the clifftop they ran off, but kept coming back which let me pick them off. I have to say, if I wasnt able to do that I would have lost.
2. I noticed that they did not build one single air unit. They did tech out their ground forces to the max, and they had tons of ultras. Almost too many though. Nice to see a variation of units though. I saw Zerglings, Hydralisks, Ultralisks, Benglings or whatever, and I think that is it.
3. The AI did not expand uncontrollably. They had 4 bases, but in previous versions I found that they were occupying all areas on the map that I was not. Lots of defenses and they had some burrowed lings defending. 2 out of 4 bases had queens.
4. The AI forces replenished quickly, almost too fast though. I feel like they should have come in maybe 3 big waves instead of 6 smaller ones. That may have been more effective.
I will post more analysis as I play against other races. Although I did enjoy 6.0 so far. Just play with what they give you. I did not build any air units myself, keeping it even. And it was a great match! They kept building men at the end instead of just sitting there!