Oh my! Only four levels? Just as well as if there were any more, things may have been broken on purpose.
Level 3 is the real killer. The spikes are really rather hard to get past. Once you do, however, the rest of the game is pretty easy in comparison. The boss at the end of Level 3 was some sort of Harpy, who was easy to dodge, and then it was on to Level 4. It looked like there was going to be a SuckySuck(TM) bit, with all the previous bosses one after another, but thankfully it was just the first one. Again. And again. And again. I must have killed him about ten times on this level alone.
After some more spikey bits (which were actually pretty easy), I finally made it to Dracula. And killed him on my second attempt. He turns into a bat after you die, but thankfully he’s not too difficult.
So that’s the first Game Boy game I’ve completed in years, and the 9th game this year so far. And the 5th Castlevania title this year too. I’ve got the second Game Boy Castlevania lined up now too!