Well I liked it, good gameplay, decent difficulty, most of the bosses are not screaming in anger hard but provide a decent challenge.
The only boss I dispised was the final optional one, who can pretty much fuck you up in three hits, so lightning quick dodging is necessary. Had to retry about nine times, not to mention the path to the boss is decked with spikes and dissapearing blocks that make up your path.
One thing I would like to note (potential buyers) is that this games levels are all connected kind of like metroid/castlevania. No loading at all!
You can also rematch the bosses for a higher level, see in this game the bosses have weak points and if you kill them without hitting it, you aquire their "Model" (much like the weapons of previous games) with a full bar (level 4). Hitting the weak point lowers their health and kills them quicker but also gives you a weaker model when defeated (level 1).
The levels equal the amount of time you have to use the OIS (Overdrive Invoke System, used by pressing the "a" button), which makes your attacks more powerful/gives you more abilitys.