Below, I have outlined reasons for this, but it is my beliefs that most of the new protoss abilities will likely go unused.
Protoss:
Oracles' cloak field ability was deleted, instead, they can scan a target area, all cloaked and burrowed units will be visible for 20s.
Tempests' damage decreased to 30 and no longer have additional damage to massive units, attack speed decreased from 6 to 3.3.
The purifier ability of mothership core has been changed to 25 damage, range 7 lasts 45 seconds from 60 damage, range 13 lasts 20 seconds.
Mothership core now have a new ugly model.
Mothership core now can move with a speed of 0.47.
Mothership core's teleport to nexus ability has been deleted.
Mothership core now have 100 shield and 150 Hp, down from 350/350.
Mothership core's charge ability now costs 100 energy, increased from 25.
Mothership now have cloak field ability.
Mothership's vortex ability now stun the units in target area for 20s and prevent any damage to these units.
The Tempest
I don’t know what the Tempest is supposed to be. They say it’s supposed to be a “long range sniping unit”, but “long range” is the only part of that description that I see them following. Sniping is only good when the sniper is able to either:
a) Take out a target of high value, or:
b) Deal some damage from a distance and then get away.
Preferably, the sniper is best served if he can do both. When can the Tempest do these things?
a) If there are high value units, buildings, or workers out in the middle of the map.
b) If the Tempest is in the middle of the map and it is in range of high value units, buildings or workers in the opponent’s base.
c) If the Tempest is in the middle of the map and it is able to get back to safety before it is run down by the opponent’s army.
d) If the Tempest is in the middle of the map in an unknown position and only through scouting can the location of the Tempest be discovered, at which point it will have gotten away.
Generally, there are not high value targets sitting in the middle of the map. Alright, maybe BL/Infestors moving for an assault, or maybe if an opponents proxy stargate fails or something – but in general, these buildings/units remain back for the entire game or until they are making a large push with them. At the point of engagement, Tempests are abysmally weak (9 dps on a 300/300 unit, slightly less than a single stimmed marine) – therefore, their “sniping” units as they progress across the map must deal a TON of damage in order to be effective.
If it is in the middle of the map, the enemy knows both the location of the unit (by the angle the fire approaches their base), and is able to run it down (due to its 2.25 speed, which is rumored to be decreasing with the latest beta patch).
And then, even if you bypass the positional problems, its damage is horrible. It takes 2 shots (on a 3.3 second CD – the highest in the game IIRC) to kill a zergling – 3 to kill a 3/3 marine or a marine with a medevac around. Really? 10 seconds of firepower for a marine?
Potential Uses
Like everything else protoss has that’s worth making, Tempests aren’t stand-alone units. That means that likely a person will have to create positions for which Tempests are good – for example by creating a forward base with photon cannons and sniping from there, or by using a ground army, or area control spells to keep anti-air from reaching the Tempests. I suspect that without changes, it’ll be a long time after HotS is out before anyone starts using Tempests in a way that makes them worthwhile – they just seem to have a lot of weaknesses which are not obvious to fix. If a person were to want to, I’d imagine that (given the heavy tech, the close position needed to do damage, and the relative expense of protoss’s tier 1 anti-air units) using photon cannons to create a forward base would likely be the best option for sieging an opponents base. Then the problem becomes “how do I keep my opponent from running around my cannons and killing everything else I have – a problem for which I have no answer (yet – trying to be optimistic here).
Small Change Proposal
You want a unit that can be called a “sniper”? Don’t make it shoot a big glowy ball with a neon sign on it’s tail saying “Tempests Thataway!” Have it deal instant damage which doesn’t give away direction, similar to marines. Now your opponent has to scout to find your Tempests, and a clever player can snipe and retreat over and over again without being detected. Now you’ve got a real sniper that functions… well, like a sniper.
Oracle
I dislike removing cloak from the Oracle. The Oracle in this iteration has no effect on the protoss army’s strength (down from a slight effect on army strength), and is only useful in harassment. There is no other unit in the game which can say this. Every other harassment unit is capable of dealing damage through spells or attacks. On top of this, it costs 200 gas and is made of a very flimsy paper (it has 100 health, which gives is the lowest health per gas of any unit in the game – even less than the Templar, Sentry, or Infestor). Players opening stargate will likely get one of these because the harassment is easy to do and can (especially in 1-base situations) be quite damaging. But (as I’ve noted above) since most players are not opening stargate now, and unless I’m missing something major (like future changes that haven’t happened yet) I don’t see many people headed over that direction anytime soon.
Mothership Core
After having used it in the Beta Custom game, Energize had to change. It allowed you to do silly things – like using Entomb every 20 seconds, keeping a ramp 3 hexes wide permanently blocked off by only building a single Sentry, or keeping 4 buildings constantly Chrono Boosted. Reports are that Energize is no longer usable on the Nexus. That may or may not be reverted, but either way, I still think Energize will make a huge change to Protoss Builds. One sentry is no longer sufficient to block off a ramp indefinitely, but it’s sufficient to block it off long enough to get additional sentries. I’m not sure if 100 is the right number (it’s effectively 3 minutes of energy) – it seems rather high.
I’m also not surprised the damage was nerfed. 60 damage a shot (effectively 1-shotting marines) proved a bit better at denying harassment and early pushes than was probably intended.
I dislike how low its health is now (lots of energy can get lost real quick if you’re not careful), and personally, I think a 0.47 speed unit you need to use effectively is going to feel weird.
Their changes also have the unintended function that (with the removal of the Vortex-Archon combo) the evolution of the Motership Core - the Mothership - once again fills no roles. Perhaps if you are able to move into the area without being stunned, the Mothership can be used to surround things with zealots or cut an enemy’s army in half “for real” (wasn’t this what it was intended to do anyway?).
Overall
Protoss is getting stronger in HotS – every race is. But, unlike the other races, I have difficulty imagining the situations in which 2/3 of the new protoss units will be used. This doesn’t mean protoss will not be strong, but it means I have doubts that the strong builds will not look terribly new. I’m sure Kiwikaki’s old Blink Stalker harassment -> Recall strategy from forever ago will become a lot more prominent in PvZ (with recall on the Mothership core, and not requiring a Stargate/Fleet Beacon/Mothership to execute), and I imagine PvP will become much more economically focused (and less about 1-base build orders), while PvT will likely remain gateway/archon focused (even moreso with Energize and HTs giving instant storms back – albeit only a few storms from 1 HT every 3 minutes).
I don’t imagine that having much of the same protoss strategies with slight buffs to each will not be strong – I just wish it were more than strong, I wish it were new.