6.0/6.11 AI has very big improvement compared with previous versions.
 
1. Better resouce management, they can replenish their force quickly, often a wave followed a huge wave, keep you constantly under pressure.
2. AI can now operate multiple expansion bases, I once saw them bulit FOUR bases during middle of the game.
3. AI has several strategies depends on player’s action and development level. They can either mass basic units to rush in the early of the game, or mass a huge army with many different units, the latter would happen if you have sufficient defence in your base in early game.
4. AI can now produce advanced unit, like Protoss Carrier.
5. I think this is a really good AI without major defects.
 
The AI would be very hard to beat in the late game if you allow them to expand or you just turtle in your base, they would gather enough resources and mass advanced unit to crush your base to ashes. So you have to do anything you can to prevent AI expansion.  Here are some advices as you are a Protoss:
 
1. Try to lay down TWO Warpgates to produce enough Zealots. This is very critical to build sufficient defence in your base, AI will attempt to rush if you have poor defence.
2. AI scout always discover your base before your first Zealot come out. After that, control your zealot to follow their scout, their base location will be revealed.
3. Continue to mass Zealots, then divide them into Group 1 and 2.
4. G1 will attack their base and draw away AI forces, then control G2 to attack their Miners, AI would return, however their economy would be affected.
5. Try to build your expansion, AI will have little chance to gather enough unit to harass your base. Now you will control the gameplay.
6. Enjoy