Yeah... and it was kind of difficult. I agree with you there; although, unlike Sonic, this series doesn't stagnate as much and add new helpers every single time. If you look at each new game, there has been some change. SotN was the first true Metroidvania, CotM was portable and a Metroidvania, HoD was the same, but with elemental attacks, AoS offered the Soul system, DoS was the same but with the persistent map/status screen, PoR offered two main chars that could team up for powerful attacks or to solve puzzles, and OoE had the Glyph system. Unlike Sonic, which has been the same basic game over and over again, each Castlevania offers a unique experience.