For some reason Castlevania: Circle of the Moon didn't really entertain me longer then 1 hour, after that it all got boring.
Take Symphony of the Night, and take away the cool Alucard with his sword, make the entire screen dark, and the result is Circle of the Moon. Allright, I'll just admit it: the real reason I didn't really like this game was the level up system, it takes too long before you go a level up, and since the stats have become more important than in Symphony, you often find your leveling up. However, leveling up isn't as fun as it is in RPGs, and in RPGs it's also more annoying then fun. I did enjoy the exploring, but often found I was too weak for every area I went to, even though I killed every monster I saw, and didn't skip anything.
Castlevania: Circle of the Moon Might be fun for people who enjoy killing the same few creatures for experience in a non-RPG. For those that prefer skill above EXP, avoid.