Lately I've been sucked into Castlevania:SotN again.
Brothers from a different mother! I too had recently played through SotN on my Chinese handheld. Those medusa heads in that "gear" room with the water STILL drives me mad. (the location where you have to hit the 4 gears till they "click" to open the secret passage). After getting an ending, I've been trying out the plethora of Gameboy games on the handheld.
After messing with the RMenu Kai update to the ODE's, I started playing Powerslave. Originally, I just wanted to test the new software, but 4 weeks later, I'm still playing through it. I find the game to have great balance and pacing along with impressive performance for a 3D game on the ole Saturn.