Castlevania impressed me greatly with its incredible visual design and music. It is amazing what Konami did in 1987 with the NES on this one. The controls are very stiff, but that's to be expected for such an old game. Challenge, i'd say it's pretty fair, this is definitely more a game of patience than one of skill, and I'm honestly perfectly fine with that since it feels rewarding to wait for the right time to make your move instead of mindlessly attempting to force your way through it.

The big fatal flaw, though, is the last boss battle. It ruins what, up until that point, felt like a well-rounded challenge.
It just pretty much leaves you with no option but to watch a video on how to defeat him and try your very best to replicate every movement in those extremely small and precise windows in which you can avoid his attack and have a chance to land an attack on his little tiny hibox, with little to no room for experimentation.

Some people would say to just use the holy water on him since it stops his movement and lets you drain his life with your whip, but that just misses the point for me; it feels wrong to use such an easily exploitable and effective tactic on a game like this, and it leaves you with no true sense of satisfaction, at least in my opinion, of course.

So the final question is:

Is Castlevania worth a try today, over 35 years later? I'd say yes.
Is it worth the frustration only to say you beat it? Not really.