Pre-orders for 2016's batch of StarCraft II DLC have gone live on Battle.net, offering the three episodes of three missions each that will form Nova Covert Ops for $14.99 / £11.99 / €14.99 all-inclusive. They'll be released throughout 2016, with a promise that all three packs will be available before December and the first some time in Spring. It's not stated explicitly, but the implication is that each episode will also be available standalone as they arrive, akin to the way Hearthstone Adventure wings work.
StarCraft II easily makes our list of the best strategy games.