While modern $99 "video pucks" like AppleTV, Roku, or Amazon are good streaming clients for NetFlix, etc, they utterly suck at playing files from a local network. Ouya + XMBC is an incredibly option for this use case, now that Boxee is gone.
Hard to beat at $35, or $29 at Best Buy right now due to a sale. That's practically sales tax on the AppleTV plus the more or less required AppleCare.
And if you're inclined to tinker, the Chromecast is a ton of fun: it's actually running a full browser engine, and you can send it a page to view. That page can then use things like WebRTC streaming.
1. Communal browsing of content - you sometimes want to browse available content on the big screen so everyone can join in. That means menus and UIs on the TV not the device
2. Controls with physical buttons have two advantages. A well-designed remote is much easier to learn and use without needing to look at it. Secondly - games controlled via a touchscreen when you're actually looking at the TV are a fairly unpleasant experience.
I do want a smart TV with a physical controller. I also want Chromecast/Airplay etc. Different beasts.
I bought a Chromecast for $40 and the Plex iPad app for $5 and can now sit at the tv, controlled by the iPad, and stream content from my HDD flawlessly.
I played a few minutes of Minion Rush on the Amazon Fire TV. It had some laggy moments, certainly not the gaming experience that they claimed it would be.
This is simply not true. Plex has been available on the Roku for years. It's one of the most popular channels.