Order of Ecclesia presents a welcome change to the metroidvania-style games of the Castlevania line, thought while the basic platformer gameplay remains basically unchanged, the small changes to other aspects shift the game from a pure metroidvania title into more of a common 2d-action-adventure region.
You don’t explore one big castle anymore, but instead smaller areas on an overworld map that once beaten unlock new areas. A side-effect of this approach is that once beaten, you rarely have any need to go back, thus reducing backtracking to near zero (one of the biggest cornerstones of metroidvania-style games).
Instead of both magic and weapons as in previous titles on the GBA, you only have magic that powers both magic weapon spells (weapon glyphs you suck out of air from enemies to acquire them) and other true spell-like glyphs. Basically, if you swing too often in short sequence, you can (theoretically) run out of the option to use your weapon, though that happens only somewhat early in the game and later most weapons don’t use much mp to hit.
The biggest change is not gameplay but story-related. While still connected to the bigger storyline of going after Dracula, it’s not the generic “a castle has turned up, go inside and find Dracula”. This time a secret organization has developed a weapon to finally slay Dracula, but something has gone wrong and one of the order members turns traitor, whom you have to follow and bring to heel.
Despite all these changes, the game is unquestionable of similar make as the other metroidvania-esque Castlevania’s. I would have wished for more adherence to the metroidvania-style itself, as the whole backtracking often forces better level design (a lot of the smaller levels feel a bit like throw-away designs), but overall the game preserves most of the strengths of these games, while keeping it fresh by allowing itself to tell a different story than most of the other Castlevania games.