Now that it is 6-months removed from release...
The dungeon maker for sure. Very underwhelming.
However, I would say that overall, maybe it played it to safe, with there not being enough differences from the GBC version. It's a beautiful game, great music, great gameplay, and the same awesome...
The biggest flaw (for the Switch version)... is just not enough new content. A good revamped trip down memory lane, but not enough new stuff.
Minor flaw... I don't like the Pegasus Boots. Much prefer how they controlled in A Link Between Worlds.