Mario always has new great level designs, if not mechanics plus great level designs.
Castlevania in the IGA age has always had pretty good combat, but outside of SotN, the platforming has been less than engaging on it's own with endless flat hallways and corridors plaguing the overall map. The combat is fine, hasn't changed much from it's basic core, and has been pretty consistent. The problem is that the combat is the majority of the gameplay, due to the downsizing on emphasis for level design. What they need to do in order to really progress things is being back some older elements like Whip Swinging, and something new perhaps, to enhance the level design and possibilities.
Order of Ecclesia started to do this, with the magnus glyph and a few others. You can even see this trend continue in Harmony of Despair, despite being a horrible game, there was a noticeable increased focus on platforming and puzzles in the level design with complementing character abilities (such as Julius and the 8-way whipping). This was definitely a step in the right direction. Mirror of Fate seems to attempt this, but the whip segments are very automated and have a distinct lack of control to them. This kind of scripted gameplay detracts from player control, and over all, detracts from the gameplay itself being the reward for the player. Less control leads to less fulfillment, and sense of accomplishment.
This also goes for the 'glowing edges' and scripted edge traversing segments. Right along with this, the context sensitive triggering of fall damage greatly impedes on player experimentation and freedom. There are plenty of ways to get around this through good level design, but they didn't follow that model. Though Mirror of Fate's approach is technically a step in the right direction, it needs to give the player more of a role in the actions like Super Castlevania IV and Order of Ecclesia did.
I believe, in terms of this, that Order of Ecclesia as a game offers more in a whole than Mirror of Fate has in series progression, especially where platforming is concerned.
This is the primary reason I really wanted to see how IGA would take this one step further to continue the growth of the series and bring it back more to the platforming roots than previous installments of the IGA era had been.