It definitely plays like an old NES game, albeit with shiny new graphics and music. The game's not a port; rather, it's more of a reimagined version of the original game. This new one has a new intro stage, new end stage, and gives a bit of a wider variety of objectives to accomplish in each stage. Maps appear in easy and normal mode to help you with the objectives, but they're absent in hard and extreme modes.
I'm actually astonished they got all the original survivng voice actors to reprise their roles. Especially the VA for Scrooge McDuck. That man's like over ninety years old! What devotion!
Really, if you like Shovel Knight, I think you'd like this game. Shovel Knight draws inspiration from the original, as well as from Mega Man (both Ducktales and Mega Man were developed by Capcom).