The Secret ambush sounds great and that's a good approach. I'd also recommend a Robo-Rush strategy. This involves building a Robotics Facility that will help you to produce Immortals. Then rush your enemy with these powerful units.Playing as Protoss in StarCraft II requires you to go for a Proxy Gateway strategy. With this strategy, you need to build a hidden Gateway near your enemy's base and quickly produce units to attack them. It's more like a secret ambush.
The Secret ambush sounds great and that's a good approach. I'd also recommend a Robo-Rush strategy. This involves building a Robotics Facility that will help you to produce Immortals. Then rush your enemy with these powerful units.