• An advantage in 2D is that the player sees the relation to the enemy or setting because there is only one full view.
  
• Pixel art is a huge part of the Castlevania series. The original series only had four colors, whereas the rest of the 2D series has 16, and sometimes 256 colors. 
• As systems get more powerful, it's harder to maintain the quality of the game. This is why it is so hard to create another pixel art Castlevania game on a console.
• Another advantage of 2D is the lack of issues with camera angles. 2D games also require a much smaller team than 3D.
• Some platforms that are viable for 2D games: DS, VC, Xbox Live Arcade and cell phones.
• Igarashi and his team are still considering making games for the Wii and other platforms.
  
• They are also exploring WiFi, and newer character for Castlevania.
  
• The last Castlevania title took 16 months to complete.
  

Via Go Nintendo