Ok, let's give this thing a spin. Don't mind me playing terribly, I always get nervous on my first time. Oh, *SPOILERS* I guess.
Now this is fan service done right. The unlikely collision of both Sonic and Zelda worlds produces a fun level, giving us a sneak peek at what Zelda could look like on Wii U. It is however very much a "Sonic Lost World" level at its core but at the price of zero rupees, you just can't go wrong with this one. I will now go play this thing properly and dream of new upcoming DLC set in "Metroid" land. Let's not even speculate how awesome a "F-Zero" themed level would look like, with Sonic running along the racing course... well played, SEGA/Nintendo. More DLC like this will be quite welcomed in the future.
Well, you can't actually "Buy It!" per say, but you know what I mean... go get those updates and free DLC's already.
*OMAKE* Here is "Yoshi's Island Zone" DLC in case you haven't seen it yet.