I haven't player much of Castlevania as of yet, but so far it seems pretty good. It has the currently popular God of War gameplay mechanic with a few small tweaks and additions. I can't really complain about it, it's a proven successful gameplay mechanism and so far I don't have any problems with it, even if it feels a tad unoriginal.
The biggest thing Castlevania has going for itself is the look of it. For one thing: the graphics aren't like "OMFG, it looks so real man!" but more like "OMFG, it looks cool as ****, man!", which I often do prefer in games, so that's a point plus. Another thing with the look of it are certain of the cutscenes. In the start of the game there's a sequence where you're riding on a magical horse, followed by big wolf thingys. The end of that game section is a cutscene where the horse leaps over a big, gaping hole in an old bridge, but the horse disappears halfway, leaving the protagonist to eating dirt as he makes a rough landing on the other side. The wolfies fall down the hole in the bridge, to their death, and the scene concludes. I mean, it doesn't sound much when I just say it like this, but when I watched it I was staring at the telly; the little voice in my head going "That was freaking awesome dude!" I'm sure scenes like that are going to occur many more times, so I am a little excited as to what's more to come in the game.
Castlevania is the kind of game you buy if you have some extra cash, or have no games to play, but it's not a game I'd buy as my only game that month, it's not original enough for that, at least in my opinion.