Got my Fire TV stick yesterday, I now have both it, and a Chromecast.
The FireTV stick is pretty cool, it's nice that it comes already set up for your account and everything, don't even have to log in with your Amazon info.
My only gripe so far is that it gave me a warning that it could not draw enough power just from having the power cord plugged into an extra USB port on the TV, it recommended actually plugging it into an outlet(Chromecast works fine powered from USB only).
Also though, Amazon Prime video service needs to do a little bit better job distinguishing between movies/TV shows that are free with the Prime service, and ones you have to pay for. You have to actually go into the episode list of a series before you can see the pricing, it would be nice if you could somehow tell that while browsing (A "free" typed on the series graphic or something while browsing would work.