Its cool.
I tried it out. The gameplay is difficult. Definitely not as smooth as Castlevania. The A and B button are swapped which is driving me nuts...and can't be swapped back. The music, the sound effects, just about everything are straight out of the NDS Castlevania games. Only graphics quality is more toward the GBA end. Some parts so far are unfairly difficult IMO. But overall still worth $5, I think.