Miiverse is great. I really like it, but for some reason I sort of forget about it for stretches. But there are some great posts there and amazing arts work and a great place for hints, tips about new games and what not.
For all the adults in this thread complaining about it being like hanging out with little kids: What are you doing on the internet at all? Miiverse is no more filled with little kids than VGChartz or the rest of the internet.