Not nearly as good as it should have been.
I really liked the story, and one must actually try to do well if one wants to see the "good" ending. I ponder why the male antagonist, who is of Belmont lineage, was given a different surname. It just seems unnecessary to name a male Castlevania protagonist "Schneider" (no offense to those of you with that last name).
The graphics were way too blurry. Yes, I know the N64 had texturing issues, but they made other games that looked way better than Castlevania 64. To me, this is another indicator of how this game was rushed to release. Still, the environments are well done, sometimes great, so I can't be too critical of all the graphics. Some of the bosses were cool, as well.
Gameplay was pretty standard, although at times a glimmer of ingenuity showed through. For example, I thought it was a cool idea to have a chainsaw-wielding Monster chase you through a hedge maze while following that lil' bastard Malus (the "child" you are trying to save). For the most part, the levels are platform and "go-fer" based, somewhat like Soul Reaver but harder to endure (see Controls gripe above).
Bad guys are dispatched with a whip (wow!) or magic, depending on your choice of character. The guy, Reinhardt, is a meat monkey while the girl, Carrie Fernandez (a descendent of Sypha the sorceress in Castlevania III for the NES oh my god I am getting old to remember that) is the magic user. The game starts out harder for Carrie, but by the end the game seemed easier because of her magical prowess. No matter who you choose, it never is that hard.
Finally, the music and sound were good. Especially the former, which is a great achievement on a cartridge-based system. If only the graphics and controls had been as good or even close, Castlevania 64 could have been great.