Damnation is essentially just a 4-mana Black version of Wrath of God. The only difference is that it is in Black, a color-shifted variant from Planar Chaos. The reason that Damnation is so good is that it can be played in non-White Modern decks such as Grixis Delver, Grixis Control, and most often Jund. It also sees play in Abzan decks, despite having access to White, since Black is an easier color to fix for in those decks. Interestingly, Damnation is rarely seen in competitive Modern mainboards, and usually relegated to a single copy in the sideboard for certain matchups. In any case, it’s still a valuable card to have around.
Damnation is particularly popular in Commander, where Black decks are quite rampant. In a singleton format, those decks that can will play both Wrath of God and Damnation. What makes Damnation better than a boardwipe like Day of Judgment is that creatures can’t be regenerated. While Thrun, the Last Troll, Troll Ascetic, and other creatures with regenerate aren’t rampant in Modern, they do see play in the format. Affinity, a very popular and powerful Modern deck, also has ways to regenerate some of their artifact creatures. Damnation takes care of those corner cases.
Since Damnation is so good in Modern, this is a great reprint to help players invest more in the format. But since Damnation is such a staple in Commander, this will also be of great use to those players, as well. Pretty much everyone is going to want this card, so get your hands on them while you can! This reprint cut the $50 price tag for this card in half, but it's certainly going to be in demand for the foreseeable future.