This is a fantastic card, and it scales even better the more difficult the scenario. Starting from a solo perspective, for the cost of ~3 ER to play and clear this, you cancel threat from step 1 of the villain phase (~0.5 ER), a villain activation (~2 ER), and minion activations (value varies). You delay the reveal of encounter cards for a turn even though you are still dealt one (difficult to quantify), and sometimes you get random stuff like avoiding a draw from the side scheme deck against Red Skull. The raw value from cancelling steps 1 and 2 is close to breaking even, and waiting an extra turn to reveal encounter cards helps you better prepare for them or clear other threats that could combo with them. That adds up to an extremely powerful combination of effects. The skipping of an activation also provides a rare opportunity to cancel a steady/stalwart villain activation from the likes of Thanos, Venom Goblin, Magneto, and Ronan - some of the hardest villains. Of course, you also get the usual side scheme combos like Skilled Investigator and Stealth Training.
There is certainly a cost to not being able to damage the villain during your extra turn as this can lead you to wasting resources if you draw a few attacks. That's why it's best to clear Run Them To Ground on an early turn, when you still have upgrades and supports to get out, or when the board is getting out of control, since you would be focusing on clearing that anyways. Especially in higher difficulties, you might not turn your attention to the villain until long into the game, lengthening the useful window.
In multiplayer, there are diminishing returns if the table has not coordinated decks to take advantage of Run Them to Ground. The scaling of the raw value is fair. For every 4 threat added initially (~2 ER), an extra 1 thwart and one villain activation get cancelled (~2.5 ER), but it is also more likely to inconvenience other players. Aggression players may significantly waste the extra turn with damage-heavy hands. Protection decks miss a villain phase where they might usually play much of their hand.
For any of my fellow Heroic enjoyers, this is one of the best cards in the game. When you skip a villain phase that would deal you two encounter cards and replace that with getting dealt one instead, you have effectively canceled an entire encounter card in addition to the benefits I have already mentioned. I have been playing the heck out of this card, and it has not disappointed.