Order of Ecclesia is the pinnacle of the series regarding bosses. I don't remember any other game with so many enjoyable bosses. It's simply the best on the series in this regard. Reason why I love it (other reason being the combat system, more streamlined and relevant than SOTN).
This. OOE owned the rest of the games with boss fights. Although I likes DOS' bosses (particularly death) and I thought POR's DracDeath was probably the best final boss fight (or close to) OOE really broke the mould with bosses, inclusive of Dracula. Plus it gives the option of a supertough setting, which is great fun.
And COTM was supposedly hard because of it's design. The way the characters control is more like the older games, even though the control is a bit better.
Honestly I thought the only thing COTM was missing was a backdash, the controls felt okay aside from this.
When I play the first Castlevanias (before Legends comes to light), I supose that the superhuman powers that the Belmonts has were form the Belmont Chromosomes (as is implied in the CVIII manual or box, I don´t remember). Then, when I played and finished Legends, and I read that Sonia have a baby with Alucard, I learned that "maybe" is because of that the superhuman power of the Belmont, from that part of the history... I accepted, but I don´t like it too much.
The issue with the Sonia/ Alucard affair is that the VK doesn't work that way, it can't be used by a tainted soul/ blood. If Alucard's blood got into the Belmont's lineage then the direct bloodline would be contaminated. I think CV III as the first showdown with Dracula fits better as well. Which is not to say Sonia shouldn't reappear in the old canon, in a later game. One could say that Legends and the non-canon games simply fit into an alternate timeline, problem solved.