The cancellation announcement came a few months ago. I loved the show through the first three seasons, but the fourth season made me embarrassed
for all who were involved with it; it seemed to me like everything that occurred was wildly out of character, especially the plotlines surrounding Sylar. Conjuring a plotline in which he yearned to become a "good guy" was utterly ludicrous and wholly inconsistent with three seasons of fine work from Zachary Quinto in making him a heartless, irredeemable bastard. And setting him up with Claire? The ridiculousness just kept escalating. I loved the show and think that there were many more stories that could have been told, but considering the direction that it was headed, it was time to put Heroes out of its misery.
On the bright side, now that the cast is free of its obligation to the show, think how much work they'll be able to do (and we'll be able to see them in) outside of Heroes. I really enjoyed Milo Ventimiglia, Zachary Quinto, and Masi Oka's acting; hopefully being let out of Heroes will allow them to do bigger and better things.