You guys are all picking the uncreative/uninspired bosses. Frankly, I think bosses that are broken are worse.
The Golem in Haunted Castle is a shining example. Depending on his height, his "Arm launch" attack cannot be avoided, so winning the battle depends heavily on how the golem is positioned, rather than skill. Without this cheapness, the golem is also a very uninspired boss, since that is his only attack, and when he's not positioned in an impossible-to-dodge way, the move is very easy to avoid. The Golem also has a common tendency of moving away from you if you jump forward, drawing out the pointless battle further. The boss poses no genuine challenge and lacks creativety. I believe that earns him the award of worst boss in Castlevania history.