It depends upon the lens through which you're viewing it. Maybe it isn't as timeless as Super Mario Brothers 3 or something, but if you look at it in the context in which it came out, it's probably in the top 10% of NES games.
The combat is difficult and satisfying in a Dark Soulsy kind of way, and the music is good. It's also kind of obtuse though. The obtuseness + difficulty makes it hard to approach today.