To be honest, I would drop the 1x Craterhoof Behemoth for 1x Wolfir Silverheart .

He makes your Restoration Angel and Sigarda, Host of Herons hit like a Craterhoof Behemoth . Plus they're flying. :D

My two-cents worth! +1 from me.

I would add 2x Garruk, Primal Hunter to the main board it provides a body per turn and any kind of draw power goes a long way in a deck like this where you can probably draw at least 5 cards off his -3 but I would also consider Thragtusk if you can afford it because he wins games and with your ability to get him back to your hand will highly affect the game and can take this deck and work it in late game which it is currently lacking so if your facing any kind of control then you will have many problems that you most likely won't be able to deal with with just a Centaur Healer alone because your opponent will let it resolve but if it is control then you have to worry about cards like Terminus and Supreme Verdict because when you try to cast sigarda or angel of serenity then it will most likely see Syncopate or Dissipate . something else that could be useful to run Im not sure if it is the best for this deck but maybe try playtesting with Silverblade Paladin works great with Craterhoof Behemoth , Wolfir Silverheart and Sigarda, Host of Herons and works great with your aggro ramp theme.

@Nivrix The craterhoof ends the game where as silverheart isn't always going to do that.

@SwiftDeath i have all of the late game. the 3 biggest finishers in standard are1. Craterhoof Behemoth 2.Angel of Serenity and 3. the only one i dont have Armada Wurm with entreat still high up there. Terminus is a pain to me much more than verdict but both i can deal with with the garruk i main board. Paladin would be a big change to the deck as i have went away from the aggro route for a bigger ramp style deck.

the late game doesnt seem to be the issue, your mid game is being carried by an army of 2's. I would -2 Revenge of the Hunted and +2 Increasing Savagery . I love revenge for it's board clearing ability, but your deck seems like it's going to need something a little bit more permanent. It just seems to pull out all of this ramp, but if it doesnt get the threats to go with it you're hosed. XD

Savagery seems interesting as I can flash it back quickly and make a dork or a keyrune massive and force blocks.