Beyond a shadow of a doubt, Amazon's Fire TV is a Roku killer. I explain why Roku simply can't compete with Amazon at the link, but -- long story short -- Roku doesn't have the guns necessary to make the emotional connection with the mainstream consumer the way Amazon and, to similar extents, Apple (AAPL) and Google (GOOG) do. Though, as you'll read, Amazon, even if unintentionally, schools Apple with Fire TV, at least in one respect.
Amazon Fire TV (I keep wanting to call it "Prime TV") isn't perfect, but that doesn't matter.
Fire TV covers the major bases -- Netflix (NFLX), Hulu, Pandora (P). Most people aren't going to care that, at this point, it doesn't have more obscure music apps such as Rdio or access to NHL Game Center or Major League Baseball At-Bat. This matters to me because I listen to Rdio (and Pandora) all day and often watch hockey and/or baseball all night. But I'm convinced these viewing habits render me an outlier.
Fire TV is Amazon Prime focused. Not a surprise. Amazon constructed the user interface to make it easy for you to make Prime-related purchases. During the signup process, you're prompted to join Prime if you haven't already. If you're already a member, it knows this and proceeds with what was, for me, a frustratingly slow setup. Amazon told me my Internet connection was slow as a software update took about 15-20 minutes to complete.