"For destruction, Ice is also great; and would suffice."
The changes made to Protoss between Starcraft Broodwars and Starcraft 2 have lead to a race with a completely different feel. Based around the Warpgate Protoss forces easily resupply in mid combat with some of the toughest units in the game. Known for valuing quality over quantity the Protoss force tends to be small but powerful.
The Protoss macro mechanic is the Chrono Boost. This ability allows any building to increase the rate at which it is performing by 50%. This includes research and unit production. As a result Protoss can quickly upgrade and progress up the tech tree or produce strong forces on the fly. This is perhaps the hardest macro mechanic to use, not because of the tension (deciding what to use it on), but remembering to use it. Especially in late games you will see Protoss Nexus with unused Chronoboost.
While back in Starcraft 1 Protoss were unique in that their buildings built themselves without the help of a worker (once started), this has further been augmented in Starcraft 2 to allow the same production of Units! Warpgates allow for the production of Gateway units (Zealot, Stalker, Sentry, High Templar, Dark Templar) anywhere on the map where the Protoss has power (anywhere they could build a building). This is further bolstered by the Warp Prism which allows power to be distributed anywhere it can move to (which as a flying unit is anywhere). The result is unparalleled map control. The ability to field a force where ever, whenever and reinforce it. This also lead to Protoss builds being heavily Gateway unit dependent. The Protoss techtree then usually looks like a thick trunk with 2 or 3 major branches. This trunk is the large bulk of gateway units, which are later supplemented by units from the Robotics Factory or Starport (or more Gateways). This also leads to a "Sim City" style of play, where Protoss players seek to produce a high number of Gateways (to turn into Warpgates). Its also worth mentioning that Warpgates decrease build times.
Protoss expansion is fairly easy because new Nexus can be warped in and probe production can be boosted by Chrono Boost. Additionally, the ever flexible Photon cannon leads to cheep but effective defense. Finally, the presence of power around new expansions means that a Protoss player can respond to Harassment almost immediately. Without having to wait on the bulk of his forces.
Protoss actually have a verity of tools at their disposal for harassment. The Charge upgrade for Zealots, in addition to providing the Charge spell, is also a movement speed upgrade. This allows your Zealots to work as an effective harassment force. Stalkers are fast to begin with, but also benefit from Blink as it allows them to bypass cliffs (in a manner similar to Reapers). Both of these are excellent harassing units right out of the Gateway, but Protoss' real harassment power comes from the Warpgate/Warp Prism combo. Warp Prism functionality is fairly straight forward: Move to an area, activate Prism to produce power, warp in units. What people frequently forget is that units can be loaded into the Warp Prism as it is a transport. This means you can drop an Immortal (or other ground unit) in the back of someone's base and then Deploy the Prism for reinforcements. Alternatively you can Deploy and warp in units and then load them up when the Opponent brings back troops to defend. The Warp Prism is a very versatile and often underused unit. Additionally, Phoenix work very effective as a harassment unit. Their ability to shoot and move provides air dominance over a number of other air units, but it is the Graviton Beam that really makes the Phoenix shine. This allows a Phoenix to lift workers so that other Phoenix can shoot them (remember workers are light armored units). Finally, the Voidray is often used as a harassment unit due to its ability to quickly destroy buildings. 2 or 3 Voidrays will make short work of a Command Center/Nexus/Hatchery often times before reinforcements can arrive. Don't send one in alone though, as they are expensive and take too long on their own.
While the Photon Cannon is known for being reliable (Attacks both ground and air and is a detector for stealth units). Protoss defense usually trades on their ability to control the map. Fast units like Stalkers (which can teleport short distances) plus the ability to make impassable terrain (Sentry), added to great anti air (Pheonix which can move and shoot) combine with Warpgate technology to produce an army that can control when and where battles take place. This ability becomes the greatest defense the Protoss have, choosing their ground. Just ask the defenders at Red Cliff or Thermopylae, you control the terrain you control the battle.
As mentioned before Protoss tend to rely on heavy gateway unit compositions with a few others thrown in. Because a given Protoss based can support 3 Gateways plus an additional building of constant production, Protoss strategies are often described as "3 Gate into Robo" or "4 Gate" or "3 Gate plus Starport". In the case of "4 Gate" this often refers to producing some sort of templar out as well. The Protoss ability to adapt is often based around what this fourth building is. This leads many to believe Protoss is inflexible in early to mid game. While this maybe true, they make up for it by having a very powerful core unit group which lasts from early to late game.
Protoss also have only 5 weapon/defensive upgrades. However, since Protoss have two different defenses (armor and shields) this often leads to just having weapons upgraded. While this can be frustrating, they make up for it by being able to Chrono Boost upgrades in progress, leading much faster upgrades. There are a few key upgrades outside of basic weapon/defense, such as warp gate or thermal lance, but their low number makes them very accessible.
Protoss Air is usually considered an after thought by many players. This is a mistake. While Protoss may lack the massive airpower Zerg has, they are not to be underestimated. For starters Protoss have the strongest Air to Air unit, the Pheonix. In additon, to being able to move while it shoots, the Pheonix is able to lift up ground units, effectively taking them out of combat for the duration, and making them target-able by other Pheonix. This strategy is very effective against high powered units like the Terran Siege Tank. Added to this, Protoss have the very scary Void Ray. The Void Ray is a unique unit in that the longer it attacks a target the more damage it does. This ability, combined with its bonus versus armored, has lead to players using the Void Ray to snipe buildings. This tactic, often employed as a rush, is most effective against Zerg who have late anti-air.