Great Game. Without a doubt my Favorite game of all Time.
Throughout your Adventure in Dracula's Castle you will come across Various Bosses, Enemies, Items, and Upgrades (If you want to call them that). There are upgrades as Double Jump, Transform into various things such as Wolf, Bat and Fog. By the end of the game you will not be the same Alucard as you started with.
There is also a sort of "Second Castle" it is the First Castle Upside Down(Harder Difficulty too I would say) with different items, bosses, ect.. spreaded throughout. You wont go through the castle the same way you did the first one due to bosses and stuff being placed differently. You can also play as Richter after you beat the Inverted Castle, he is a real pain tho. He doesnt level up, get new items or anything like alucard. It is pretty challenging.
Overall if you liked other castlevania games you should go ahead and get this whenever you can. Whether its on the PS1, Sega Saturn (***. Only), Xbox Live, Playstation Network or Castlevania Dracula X (Which has Castlevania SoTN in it).
This game is easily Masterpiece!