Deathcap is one of the perennial caster items in League of Legends. Not only does it give an enormous amount of ability power, but it also increases all of your ability power (including what it grants) by a whopping 30%. This seems so ridiculously powerful! Even though it's expensive, 30% increase in AP is such a huge boost to damage that it can't be beaten.
Is this really the case, though? In Summoner's Rift, I completely agree that Deathcap is a great item. In Twisted Treeline, Wooglet's Witchcap (the replacement item for Deathcap) is also incredible. However, in Dominion and ARAM, the fast-paced action and frequent conflicts change the nature of the wizard hats considerably.