I've summarized it down I think to these points.
 
Buy this game if you like: Actual Castlevania gameplay but without a straight XP-leveling mechanic, loot-lust, 2-D multiplayer action, light RPG min/maxing elements, really challenging 2-D platforming.
 
Buy this game if you hate: Castlevania storylines, the room change animations form previous Castlevania games, inverted castles.  
 
The Baseline: You better be a pretty die-hard Castlevania fan that doesn't mind the fact that there's not the typical singleplayer experience here, due to the missing storyline and missing castle exploration elements.
 
[edited after spending many hours into the game] 
 
I've summarized the rest of my thoughts to a blog. Link incoming.

Aww man, I hated the oldest Castlevania games but was really looking forward to this one. Maybe I'll get the Symphony remake on PSP instead...

I've never played a castlevania game except for the demo of the first xbla one. I love this game. :] Also loot lust doesn't count. Well for my character anyway, I just bought the best equipment in the store so far and i havent found anything better yet. It's more about level up lust. One more skill, one more spell, one more power up. I get excited every time I see my fireball spell do one more damage.

The way that I look at it is that I'll only get it if a few of my friends get it for the co-op fun.

Ok so, buy this if I don't like Castlevania, but like Castlevania... 
 
wait, what?

I was on the fence when I saw "Play the new Castlevania ADVENTURE" on my dash, then I saw the quick look and realized it's not an adventure at all. 
Almost everything I enjoy about Castlevania games has been removed from it.