The first Castlevania for the Gameboy suffers from similar problems as the Castlevanias on the NES. The controls are extremely unforgiving. Trying to jump in the game becomes a real test of skill, since your jump ability is very limited. Often you have to time your jumps pixel-perfect, or you’ll fall to your doom. Despite these serious shortcomings, I actually enjoy the game.
Unlike in the NES-version, where the variations in the attack patterns of even minor enemies made the game slightly unpredictable, the GB-version has none of that. Playing the game is like a very big memory test. Enemies attack nearly always in the same way from the same position. That makes the game moderately easy in comparison to first and the third NES-Castlevania.