I haven't played Castlevania, yet. My take on it is this: God of War 3 is about ten hours long. It was an amazing ten hours, for me. As great as those ten hours were, they are over. Castlevania is a viable option for people that want to play something similar to pass the time until God of War 4. There's a ton of options in that department: Conan, Bayonetta, Dante's Inferno, Devil May Cry, etc. for fans to try.
So, instead of assuming that game A is better than game B (which is a matter of personal opinion, no matter how you look at it), let's just say that people who like game A will probably enjoy game B, too. It doesn't have to be better than the game that a majority will always feel is the best (this goes for any game that tries to knock Mario, Halo, or Gran Turismo off of their perch, too.). Save the comparisons for when Gears of War 3 faces off with Uncharted 3. That's when it will actually matter.
