Underrated. Not a perfect game by any means, but a good first 3-D effort for Castlevania, and Legacy of Darkness helped flesh the base game out still further. Of course, it was also one of the small handful of third party N64 games that was anything resembling decent.
I agree, it might not have aged in stellar fashion, but in 1999 it was a very good adventure. I also agree, that in a sea of mediocre 3rd party efforts Castlevania 64 was a legitimate AAA game from Konami on the system, and as such I was thankful. To be fair for Goemon Mystical Ninja was also a pretty darn good game from Konami for the system.