Trine 3: the Artifacts of Power, in its current state, is an unfinished game. Priced at $23.99 with little chance of completion, and no confirmation from the developer on whether the story will ever be finished, the result is a tough sell. And one that I can't recommend buying into.
Placed alongside Endless Legend's previous expansion, 'Guardians', Shadows is similarly priced and has a lot more to offer in the way of content. How that content is introduced to the player could use some work, but the amount given is neither too much nor too little.
Even before any consideration of steam promotional discounts, it'd be a gross mistake to say that Dropsy isn't worth the price of admission. For fans of the point and click adventure genre, aficionados of retro pixel artwork, or anyone looking to get lost in a kind of feel good world that warms you when it's not frightening you, this is a steal. Come on, give the creepy clown a hug.