The other obvious comparison is to Coercion. One frustrating thing about running Coercion (or Duress, or Cabal Therapy, or other cards in this family) is that often there are multiple cards you see that you don't want to deal with. At other times there's nothing worth taking, or even nothing at all. With Nightmare Void you can choose when to continue the attack on their hand and when to move on to more pressing matters. If you want to, each turn you will draw a spell that will trade with a spell that you don't want to face. Eventually this will leave them with a hand that is empty of anything you deem to be relevant. A lot of decks are not comfortable living off of the top of their library for the entire game. If they start holding cards again in the future, you can go after their hand again.
As a control deck there is little you can do about this type of assault without going after your opponent's graveyard. First I will draw out all of your counterspells. Next I'll take out all of your mass removal and win conditions, paving the way for my creatures. In the long run, it is very hard to win this battle. Their opponent can store up threats in his hand but any time they try to hold answers those answers can be traded off. Every time that happens, not only do they lose important cards but their opponent made sure he wouldn't draw any lands.
The best argument against Nightmare Void is that it can't give you the type of advantage that Disrupting Scepter could have. The next best is that it seems like an inefficient use of mana and a loss of tempo. A third would be the existence of other, more threatening discard spells like Persecute. It's hard to run multiple four mana cards that try to do the same job. These are fair objections, but Nightmare Void has two huge advantages to compensate. The first is that unlike other repeatable discard it requires no investment. Disrupting Scepter gives your opponent plenty of warning before the key cards go away. Even Hypnotic Specter gives your opponent a turn to react. Nightmare Void hits right away and hits hard. Persecute is powerful, but it is not repeatable discard and that brings us to the second point: This is the only discard spell that can take out a hand full of counters despite the opponent having the mana to cast them. In the matchups where this is most valuable, your opponent can stop it once or twice but can't do that forever.
In a way, Nightmare Void is the ultimate test spell. You have to counter it, but when you counter it I lose nothing by casting it and will lose nothing by casting it again. When you want it the most, Nightmare Void is invaluable. There are strategies that cannot defeat four mana and a Nightmare Void. They might be drawing extra cards, but eventually they will end up with no relevant spells because you took them all. When it doesn't do that much, it doesn't cost you much either, and while you are doing it you can set up other dredge spells to finish them off knowing what will be effective against them. An important point to remember is that multiple dredge spells can feed off of each other, and this one is great for doing that. You clear a path and then choose what can go through that path. Grave-Shell Scarab and this are a nightmare and fit well into the same deck. Use mana acceleration to get to them fast, then ask your opponent questions for which there are few permanent answers.
For tournament players, you can maindeck Nightmare Void without much risk, but it will likely be most valuable out of the sideboard to hit those players who don't want to see it. Effective sideboarding against permission decks is difficult. You can find good spells that you want to cast, but those spells are not much good for you if they don't resolve. When they do resolve often they end up trading for various kinds of removal anyway. If you can resolve a Persecute you will devastate a control player, but getting Persecute countered and getting Diabolic Tutor countered are exactly the same. Getting Nightmare Void countered is a giant leap ahead of both of them.
When you want it the most, Nightmare Void is invaluable. There are strategies that cannot defeat four mana and a Nightmare Void.
A lot of people think time has passed blue by, and that such decks are a thing of the past. I've thought that several times, but it never works out that way. Control is a powerful strategy and one of the things keeping control in check was that players prepared for it. Every time a deck was built, the question was asked: Am I vulnerable to permission? Am I vulnerable to control? Which cards would such a player have to stop? If there were more than eight cards that could be disregarded, players had to seriously rethink their strategy. As Counterspell, Forbid and Dismiss turned into Mana Leak, Hinder and Rewind, the control strategies seemed weaker so they were largely ignored… and then they go and dominate events like US Nationals and work their way into the top eights of Kamigawa Block Constructed tournaments. Even if your opponent's base is not blue, Nightmare Void can still rip their game plan apart so long as they're depending on reacting to your cards.
Just as sideboarding increases the power of Nightmare Void, so does going back in time. You can use Nightmare Void in Standard right now, but it starts to be a real beast in formats like Legacy. As a Landstill player, I'm dominating a deck like Goblins with plans that require many turns where there is not much action and the reason for this is what I can hold in my hand. Imagine what happens if on turn four he sacrifices a Bloodstained Mire, gets a Badlands and casts Nightmare Void. I might be able to get large amounts of card advantage off of Standstill or Fact or Fiction, but that is not going to matter. I won't be able to protect Pulse of the Fields, I won't be able to protect Wrath of God and after a while he will use Pithing Needle to nullify Circle of Protection: Red knowing that I don't have a way to stop him: If I had Disenchant, he took that away from me too. In fact, it's an open question which decks I can beat at all once they get this monster going.
Vintage is a harder case. The card has excellent utility in a number of match-ups, but you have to compete against cards that set an obscenely high bar. When players pay four mana, they tend to be using it to set up something that can dominate the entire game. Four mana sorceries are not just on the high end, they can end up being liabilities due to the threat of Mana Drain. Trading this off for Counterspell is good in the long run, but trading it for Mana Drain will often walk you into game-ending effects like Mindslaver or a giant Yawgmoth's Will. It therefore seems highly unlikely you can make the cut there from a top deck, but this could still be an interesting guerilla sideboard card for some budget strategies. Often Vintage decks have a strange weakness: They have a lot of ways to manipulate their libraries and draw extra cards, but afterwards they don't do all that much if things don't work out. This could end up attacking them in exactly the place they are most vulnerable. It's a long shot, but something to keep in mind.
The other possibility is to turn this card around. I've been using this card to combat control decks, but you could also use it in a control deck. Over time, decks fighting against control end up with cards that they can't properly take advantage of, or try to build up to one massive turn. They also can seek to win wars of exhaustion on occasion. This card can finish them off for good, and give you something active to do that encourages them to overcommit to the board. Casting this with Wrath of God as backup is hard to recover from when you can continue to recast this if your opponent doesn't bring the pressure.
The synergy of Gifts Ungiven with dredge is wonderful. Not only can you use one to go directly into the other, but the dredge effect will put cards in your graveyard that help you with recursion effects and spells like Goryo's Vengeance if you are still playing them.
No one is saying that Nightmare Void should go into every black deck, or even that it should go into every black sideboard, but it is a valuable tool to have in your box and one you should remember is out there for others to use. If you are caught unprepared, the game might take a lot of turns but be over before it starts.