I will be interested to see what Amazon announces. As someone who has both the Chromecast and Apple TV, I really think the it will be hard for Amazon to enter this market. If it is just another set top box or dongle that streaming Netflix, Hulu, HBOGO, etc. than I am not sure how they thing they are going to get people to buy it. However, I am sure they will offer some incentive for people to use their device, like this ad-supported streaming service that is being rumored now. Also, we have seen a controller so maybe Amazon will put an app store on it. Personally, I just want to see Amazon Instant Video on more devices (like the ATV). I just want one box that lets me access any content I want, and has a nice UI. I believe Apple will provide the best UI, and if they bring the app store to ATV then it's game over. Until then, I hate that they don't let anyone with competing stores on the device.
Also, I would like to see more features concerning using an iDevice to control the ATV. I think it would be cool if you could launch content from your iDevice and have the ATV stream it, like Chromecast. AirPlay is nice but I hate how drains your battery and sometimes if you leave the app it just stops. It would also be cool to be able to route the audio from your tv to your iDevice so you can plug in headphones, like with a Roku 3.