4 should be pretty doable and easy to pick up, the difficulty doesn't really get going until the first quarter of the game is through. The first one, I just recommend patience, you're going to die a fucking LOT, but remember it's a program and totally deterministic, look for patterns and try to play smart. Early Castlevania is a very deliberate and kinda slow action platformer, which sounds weird but if you consider it like a rhythm/puzzle game mentally you'll get into a groove