Against Terran you need a fast robo to get observers since they are your only protection against cloaked banshees and you need fast immortals or you WILL get raped by their marauders if the terran knows how to play.

   Against Zerg you need robo to get scouting since you won't have map control and you need fast immortals to deal with mass roach.getting an observer early to scout for spire is also extremely important.

Not until after you have at least one robotics facility is it viable to get a citadel since even with the upgrades, your units will be too weak to deal with the enemy without tech support. (And protoss are supposed to be the strongest but most expensive -_-)

   In PvP robo bay is also the by far best choice for teching since the immortals rapes stalkers and the observer lets you scout your enemy fairly early on. You can go stargate => Voidray, but that's only if you all-in.

Templar tech would be viably if psionic storm didn't suck and if you could get DTs faster. Starport needs units that are not raped by the basic enemy air units (Viking > Phoenix? but aren't protoss supposed to.... nevermind)

Except the goal of the Xel'Naga was not to create slaves. In fact it's said that they cherish all life, even whatever fucked up life they create. Their motive for creating races is because their own race was dying and they needed a successor, as pure as possible.

As for the Protoss game thing, they have explicitly stated that the campaign will be all terran and have just a few protoss missions for some sort of sense. Considering what Zeratul is supposedly doing, he seems to be relegated to exactly that duty until the next campaign or  two.

Blizz are updating Battle.net... I wanted to play!!! I'm also curious to see what they'll change.

Lore ahead.

Where is it said that they cherish all life? Considering they left the Protoss in the middle of a nasty civil war with nothing more than an "Oops, our bad!" seems to contradict that. Regardless, you assume that the threat posed is a direct battle threat. They could simply be coming back to finish their experiment which could have some very nasty implications. You seem to be idealizing the race for some reason, but the lore points to them viewing lower species as little more than toys.

My friend's book. I can find you the quote online I bet.

I also agree that they don't do mcuh for other races other than observe them, but they would never be a "threat" that kills other races. From the perspective of the SC1 game, there is absolutely zero reason for the Xel'Naga to be any form of bad. I also wish Blizzard hadn't pussied out and made them a playable race, them or those hybrids.

Edit: 2nd paragraph of http://starcraft.wikia.com/wiki/Xel%27naga

Yeah I saw that. Seems a bit of a contradiction to me, but whatever on that front. I double checked right after the post. Still, you seem to assume that the threat everyone is worried about is the Xel'Naga killing everyone. First off, this information all started with Kerigan. The woman who played everyone in the galaxy and managed to take over the Zerg. Not exactly what I am going to call a "reliable source" for real threats. And again, this could be the conclusion of the experiment which could cause all kinds of shit for the general Protoss and Zerg from just internal strife.

Also, hybrids are the Xel'Naga essentially. Purity of form + purity of essence = Xel'Naga. It might have been cool to have them as a race, but it would be hard to make them work and still feel like Starcraft. Plus if they weren't overpowered they wouldn't fit the lore. Could still exist in the single player though, and probably due to some extent.

I thought the info came from the little drawings Zeratul found in the movie thing, not Kerrigan. I just feel like they are adding more things on SC's plate when there is plenty to resolve, mainly the zerg.

As for the Xel'Naga or the hybrids being overpowered, that's not true at all. The zerg drove them off and killed a bunch during the revolts, and the Zerg nearly wiped them out before the Zerg even had some of the cooler species in them. If anythign they sound all sorts of underpowered.

There has been a bit more expanded on it I believe. My understanding is Zeratul found that on a Zerg controlled world after a short meeting with Kerigan. She essentially says the same thing though. She senses the Xel'Naga coming, and it means trouble. This really isn't adding anything to the lore of Starcraft though. It is resolving the Xel'Naga parts of the lore which are kind of critical. Especially to the hybrids.

The Zerg did manage to beat them once, but Kerigan seem concerned by their return. Given her psychic abilities there would be reason to back her fear. More to the point, you would have to give the units the feel of the Xel'Naga, and they are definitely larger than life. Anything short of ridiculously powerful would seem out of place I think.

Purity of Essence, eh? 

Sorry about that! But you should be preordering so you can get in the beta :p