In Reply To #2
I only mean the core gameplay (exploration, upgrades, XP). Otherwise, especially in Aesthetics, it's completely different.
Basically, take Metroid's shooting and CastleVania's leveling up system, add innovative twists (attacking enemies in background, flashlight eliminates being in the same room searching for item X for 10 minutes).
Despite some reviews (cough, 1up, cough), it's much more than a simple clone. It actually refines much of the formula for the better while maintaining a compelling experience.