I fired it up last night and beat the crab boss on my first try that time and played an hour or so after that. The difficulty isn't unreasonable. I'd put it on par with Circle of the Moon probably. I just have little patience for memorizing boss patterns these days, so that's where I get annoyed with them. But they're not cheap thus far.
I think my gripes are mainly inline with the above posters. It just doesn't feel like a metroidvania with the overworld, village and villagers, smaller dungeons etc. I'm also not big on the glyph system. Too many combos just do the generic combined attack. And it sucks to experiment with the joint attacks since they use a lot of hearts. I mean you can try them in the village near the heart refill thing to see what it does, but I'd like to be able to hit enemies with them and see the damage they do.
It also seems that the leveling is different. I haven't noticed my HP, MP or my attack stats etc. going up when I level up just when I find Max Ups or put on new armor/glyphs. Unless I've just missed it (i.e. it only goes up every so many levels), that seems to make grinding a bit pointless. In CoTM I'd just grind near save points when I was having problems with bosses and get my stats up.
All in all, it's not a bad game. It just doesn't feel like a pure Metroidvania game. But it's a catch 22 I guess as the series was getting a bit stale for me, but I never liked the old style Castlevania games and only got into the series with SotN. So I guess this franchise may just have to join the Nintendo franchises of games I used to love that just wore out their welcome with me from playing too many of them over the years.