Quick Edit: A poster by the alias of "JunCurium" has posted an interesting idea regarding what this post is all about and I suggest that everyone reading this post checks it out after/before reading this, thanks! (Post #17 on the first page) Also. Here's a link to a thread that is also regarding this topic, enjoy!
Lets begin with other class abilities:
Druid – Naturalize. (1 Mana) Though this ability awards your opponent 2 cards for using it, in a clutch moment it could possibly save your hide and because of it's insanely low cost, I'd say that, in certain situations, it's worth it as it, indiscriminately, destroys any targetable minion you need destroyed.
Hunter – Deadly Shot. (3 Mana) The randomness of this ability hurts it quite a bit, but considering it's cost, it might actually be worth the hassle as it also destroys any minion. In some cases, the randomness of it can actually be a blessing. Say your opponent has only 1 minion (a stealthed minion), this ability bypasses that stealth.
Mage – Polymorph. (4 Mana) Though it's a tad expensive, it indiscriminately pacifies any minion that you need it to, as long as said minion is targetable. And it's honestly quite demoralizing when your big, threatening minion is turned into a cute/fluffy, white sheep...
Paladin – N/A. Though Paladins don't have any HR (Hard Removal) abilities, they do have a few tricks up their sleeves. Humility, Aldor's Peacekeeper and an interesting combo in the form of Equality and Consecration. These abilities definitely make it much easier for Paladins to deal with sudden threats in a pinch.
Rogue – Assassinate. (5 Mana) This is (IMO) by far the best HR ability in the game thus far. As long as you can target it, Assassinate destroys any minion, indiscriminately. It's a tad expensive, but considering it's affect, I'd say it's worth it.
Shaman – Hex. (3 Mana) Like Polymorph, this isn't actually removal, it simply pacifies any minion you wish, as long as you can target it. And like the Polymorph, it's just as demoralizing to have your big, threatening minion turned into a helpless, green frog (at least the Frog has Taunt?).
Warlock – Siphon Soul. (6 Mana) This is indeed expensive but it, like Assassinate, indiscriminately destroys any targetable minion you need it to. Aside from this, Warlocks also have Twisting Nether, but that's something else entirely.
Warrior – Execute. (1 Mana) Though this ability does have a rather interesting condition, damaging minions is fairly easy to do. With this mind, I'd say that this is the second best removal tool in the game as it, indiscriminately, destroys any targetable minion that you need it to, when you need it to.
I left Priest to last as it's the focus of this article. Shadow Word: Death/Pain, Holy Fire/Nova, Shadow Madness, Mind Control and the Auchenai Soulpriest + Circle of Healing combo. Nearly all of these abilities are insanely expensive... SW: Death and Pain are the only cheap abilities to cast, and for good reason, they're severely limited.
SW: Death (3 Mana) requires the minion to have 5 or more Attack and SW: Pain (2 Mana) requires the minion to have 3 or less Attack, leaving that 4 Attack as a “sweet spot”. This opening is massively damaging to the priest as it makes it next to impossible to kill these minions, some times.
I was playing, as a Priest, against a Priest, and I had played a Sunwalker. I buffed the Sunwalker with a thought stolen Divine Spirit and then it was MCd by the other Priest. He/she then buffed it's health again with their Divine Spirit, and it took me a good 3 or 4 turns just to chew through it's health... Needless to say, this minion (my own minion) dealt a good 12 to 16 damage to me before I managed to kill it. How this is fair, I don't know. (Before y'all say “you should have MCd it back”, I would have if I had it, but I didn't...)
This isn't the only instance in which 4 Attack minions have severely screwed me over, just about any 4 Attack minion, even a Warlock's Succubus, is simply really difficult to deal with. The reason for this is our other removal. Holy Fire, aside from MC, is a Priest's only reliable removal as it, as long as you can target it, indiscriminately deals 5 damage to whatever minion you need it to and then heals you for 5 health. This (Holy Fire) is just about a Priest's only way of dealing with minions like the Chillwind Yeti, however... it costs 6 Mana... (Like a Warlock's Siphon Soul)
Holy Nova is a great ability, but it's fairly expensive (5 Mana). However, not only does this ability deal damage to all enemy characters, but it heals all friendly characters as well. This ability has saved me more times then I can remember, but it's so tricky to use as it only deals 2 damage. The reason as to why this is a problem is simply because of how the Meta-Game currently is. Everyone's using cheap costing minions with 3 health that buff other minions... Yes, this can be buffed with Spell Damage, but it's fairly impractical to have Spell Damage in your deck simply for 1 ability, perhaps 2. Even then, we'd have to first acquire said Spell Damage minion, and then be able to cast both that minion and the Nova in 1 go or else the SD minion would get killed and the combo would be lost.
Shadow Madness may only cost 4 Mana, but it doesn't actually remove anything from anywhere. If your opponent, as a Priest, has a 3, or less, Attack minion on the field, you can temporarily take control of it with Shadow Madness. The minion gains Charge and you're free to attack whatever you want to, as long as it isn't stealthed. This can be used to “kill two birds with one stone”, but can be tricky. Taunt can get in the way and it's also not able to target 4, or more, Attack minions...
Mind Control is, by far, the most hated Priest ability, understandably so, but realistically... it's the Priest's only guaranteed removal, and it costs 8 mana... Like Shadow madness, this ability is a way to deal with 4 Attack minions, but at such a hefty cost (that is only going to get even more hefty (nerfed to 10 Mana)). Not to mention that it can't target stealthed minions or the Faerie Dragon.
And lastly, the ASP + CoH combo. This combo is by far the best way for a Priest to deal with 3 and even 4 Health minions in mass numbers, it bypasses stealth and the FD's shield but, it hits your minions as well and is hard to acquire. This combo, like the Paladin's combo, is left completely to chance and is, more often then I can count, the only thing that will save my hide from certain defeat.
By turn 4 (for 4 Mana) a Priest, using this combo, can completely wipe the board, excluding the Soulpriest, (assuming the minions don't have more then 4 Health) but is left completely to RNG to actually get the combo. Why Priests have to resort to such gimmicky crap is beyond me (the same is true for Paladins).
I simply feel that the Priest class is weak and needs to be re-worked (buffed) a tad to be more consistent, removing such abilities as: Divine Spirit/Inner Fire, Cabal Shadow Priest/Lightspawn, etc... For abilities that make sense and can be relied on. I could go on and on regarding this topic, but I feel I've babbled enough. If you've got to this point, I congratulate you and I hope you agree with me.