Pros:
- Fastest building race.
The Protoss are unique in that they do not build things but rather teleport them in from their home world. When building, a probe only has to start summoning a building and can then move on.
The only limitation is that buildings have to be placed within the realm of a pylon. With that said, a single probe can build dozens of buildings at a time provided there are enough minerals and pylon space is available.
- Strong mid-to-late game
Protoss have a lot of great late game units and are able to put together a formidable army if given a few minutes to prepare. They can also summon a new army very rapidly with Warp Gates.
- Best defensive structure.
The photon cannon is the best automated defensive building in game. It is the only building that is a detector and can attack ground units. It is also the only automated building that can attack air and ground units. At 150 minerals, this structure can single handedly stop many forms of mineral harassment such as dark templar and reapers.
Be careful not to build too many of these though; many players fail at Starcraft 2 Protoss strategy as they rely too much on Cannons and not enough on units!
Cons:
- Slowest starter
This is by far the biggest weakness of the Protoss race. Protoss are very easily rushed. Gateways are slow to build and zealots are slower than other races' ground units such as Zerglings and Reapers.
Even if you have Zealots, a skilled opponent will run circles around them with ranged or fast units. Most players find the best Starcraft 2 Protoss strategy is to grab 1 Gateway and then a Cybernetics Core so they can squeeze out a fast Stalker.
- Easily harassed
This goes hand in hand with the slow start. It is easy for players of other races to wreck havoc on Protoss mineral operations. Zerg players can pump out Zerglings early in the game and attack probes while running circles around Zealots. Note that you may have to use your Probes to fight off a Zergling rush!
Additionally, the Terran unit, the reaper, can cause major damage to probes in a short amount of time.
There are two things the Protoss player can do. He can get a few cannons in his mineral base; the only downside is that this will slow down unit production and tech advancement.
Alternatively, the Protoss player can quickly tech to Stalkers (to "tech" means to quickly build buildings that allow the player to produce late game units). The downside to this strategy is the player will be open to a Zergling rush during the tech period.
The only way to be safe is to scout your opponent. If you see he is rushing to Zerglings or Reapers, you should build cannons or Stalkers as appropriate.
Throughout this Starcraft 2 Protoss Strategy guide, you will find a variety of useful tips that will help you make up for the Protoss disadvantages along with a variety of Starcraft 2 Protoss Strategy tips to help you crush your enemies.