I don’t know about you, but I have always considered “slow” to be a fairly sub-optimal power. Of all the things I can do to my enemy, slowing him down a bit seemed like the least useful. Some of this must come from starting in Asheron’s Call, where there were no slow powers (or any crowd control to speak of, when I played). Mostly, it comes from most enemies’ living only a few seconds. In the time that I could slow him down, I could blow him up.
Lately, though, I have been seeing a lot of value in it.
Slow is like a poor man’s crowd control, with bonuses because it is poor.
Crowd control provides damage mitigation and makes combat management easier. The golden standard of crowd control is referred to as a “hold” in City of Heroes (and I will be using CoH terms in this; what exactly a “mez” does varies from game to game). It makes the enemy unable to move or act, and it stops any active powers. Other forms of crowd control do this fractionally or with variation, so an immobilize/root stops movement while a stun/disorient does the rest, a sleep/mez is a hold that breaks on damage or heal, etc.
Immobilization of any sort is very convenient for fighting. It lets the squishier characters stay out of the usually-more-damaging melee range while keeping all the enemies in place for AE attacks. You do not have characters spinning around trying to stop dancing Carnies when they are all nailed to the floor.
Anything that keeps your enemy from acting is good for damage mitigation. I rarely hear crowd control referred to in terms of damage mitigation, although the words amount to it. Some thoughts on damage mitigation:
Standard damage mitigation combines three things: defense, resistance, and healing. If you have high defense, your enemy cannot hit you, so there is great value to defense buffs and accuracy debuffs. If you have high resistance, your enemy’s attacks do less damage, so there is great value to resistance buffs and damage debuffs. Healing eliminates the damage after the fact, as would a regeneration buff. All of these reduce the amount of effective damage you have coming in.
Another straightforward way of preventing damage is preventing the enemy from attacking. Duh. That is how Controllers, Dominators, and other crowd controllers keep you alive: they stop the enemy from blowing you up. I have seen many calculations of defenses that completely neglect this point. They consider the effects of various buffs and debuffs, but they do not include the potentially hard-to-calculate value of a */Dark Armor Scrapper’s fear and disorient armors. Remember: your enemy’s damage is 0 if he cannot attack you.
This brings us back to slow as the poor man’s crowd control. Many power sets have a slow of some kind, sometimes as a secondary effect (Ice Blast, Warshade blasts), but frequently as an AE attack in a Defender primary, such as Lingering Radiation. There are two distinct powers that are both called “slow,” largely because many powers that have one have both. These are a speed debuff (often packaged with a jump and fly debuff) and a recharge debuff.
The first of these is obviously your poor man’s immobilize/root. It would be called a snare in another game. Depending on the game and how you fight, the value can be minimal, particularly outside PvP. Frequently, the enemy will be right on top of the melees, and he is not going anywhere. Since I already went over when an immobilize is useful, we can skip that. Do note that a high-value or stacked snare can be an immobilize or all but (CoH hard-coded a limit on slows to keep that from happening).
The second part is the more interesting. Would you rather have your opponent held or slowed (-recharge)? All things being equal, a hold is obviously better. Are all things ever equal?
Holds and slows keep the enemy from attacking you in very different ways. If an enemy is held, he cannot use his powers, even though they are sitting there ready to activate. If an enemy is slowed, he is free to hit the button all he wants, but the power is not available. Why does this distinction matter? Because either one can keep an enemy from ever attacking again.
How often do you successfully AE hold everyone in a group as the first attack? Pretty rarely, especially since someone other than the Controller often pulls. This means that the enemy, potentially every enemy in a large group, gets a first round of attacks off. Let us assume the first attacks have happened. If you hit the enemy with a hold, you are really just getting an expensive immobilize for the first couple of seconds. Most enemies have few attacks without a great recharge. While they are held, their powers are recharging; when the hold wears off, the enemy can attack immediately. Indeed, there used to be a bug whereby being disoriented would make an attack recharge instantly, making a short disorient worse than none at all.
The hold only decreases the number of attacks if it lasts longer than the powers’ recharge length. A slow instead extends that recharge length, and the enemy is as good as held if he just has to stand there and wait to die. If all things are equal, either one will probably eliminate the enemy’s ability to attack for a few seconds, depending on when in the recharge cycle you hit the hold/slow and how fast the powers recharge. A hold is more useful against quick attacks, and a slow keeps that one big attack from ever coming back.
But wait, Cryptic has repeatedly nerfed AE holds, while adding useful secondary effects to AE slows. All things are not equal. Not too long ago, the duration of all AE holds was halved while their recharge times were doubled. Ouch. Then ED reduced your ability to extend the hold time or shorten the recharge, notably with the loss of perma-Hasten. Meanwhile, many enemies require multiple holds to be held (high magnitude), while very few have any resistance to slows.
Look at your power list. How many power sets have some form of status protection, either for you or for your teammates? Those all break holds, every single one of them. Every character going into PvP brings Break Frees to deal with holds. How many tools do you have to deal with slows? Some power sets do, but not nearly as many. Do you remember which Defender/Corruptor sets can grant protection against slow? Does Clear Mind, Increase Density, or Thaw do it? Are you going to call for that power when slowed or just tough it out, since the Defender has bigger things to worry about?
The best damage types in the game are Psionic, Toxic, and Cold (at least in PvP, but for a lot of PvE, too) because they are the least resisted. Even if you do huge Smashing damage, almost anything that has defense or resistance has it to Smashing and Lethal. Everyone expects to see holds; few people are well prepared for slows.
So instead of getting a power that has many countermeasures and many nerfs, you get something virtually ignored. An AE slow has a good recharge time, and because they are usually cones you can even increase the area of effect with range enhancements. A good slow will eliminate attacks, which is the same thing as a massive defense or resistance buff.
When is slow not useful? If you could take out an enemy in the same amount of time, do that instead. Most classes that have AE slows do not have that option, but some Corruptors will. If you have very few enemies, minions, or generally anything that will drop quickly, the slow will not do much; then again, neither would a hold.
When is a slow very useful? When you are fighting a boss who has a huge slow attack. When you are fighting a dozen minions who would otherwise get to attack several times before you get to them. When you do not have much downtime between groups, because the AE slow recharges much more quickly than the AE hold. When you are fighting one of the few enemies that just cannot be held (is it possible to lock down a Giant Monster class enemy?). In PvP.
So, your thoughts? Endurance drain is another power that works as non-hold crowd control, although that has been nerfed recently. It has the same few-defenses value that slow does, but it has the same problem as a hold: it is all or nothing, and since the power recharges constantly, it only needs to have endurance for one instant every few seconds. You need a good endurance recovery debuff to go along with that endurance drain, or else the enemy will just attack when the next endurance tick comes along.