Okay, I played three of the main stages, and I have to say that this game 1) looks and sounds lovely, 2) rekindles a lot of positive nostalgia I have for the NES version, and 3) has more negative changes than positive ones.
I like the retooled bosses (original bosses were too boring, these are pretty good) and the new audio and visuals, but this is the same 2-button gameplay we had before, and there is virtually nothing new about the stages or basic gameplay/ The new material, like the voice work, brief cutscenes, and opening bit in Scrooge's mansion, is ultimately not worth it and bogs the game down rather than enhances it. If you own the original cart and are thinking about this, try before you buy.
But do I like it? Sure. The bosses are nice, the voice work is a little much but occasionally charming, and there might be some cool endgame stuff I haven't encountered yet. I think that this game has aged decently, but I wish that a full $15 remake would have added some twists or new stuff that is both interesting and beyond cosmetic. So far that wasn't the case. I still like DuckTales, but this new one isn't new enough.
EDIT: and please, this game was never hard and still isn't hard. Every single Mega Man game ever made is tougher. The new bosses are harder, but those old bosses NEEDED an upgrade in difficulty.