There's issues like loading times that they're fixing this month, also apparently you have to add someone to your friends list
through miiverse and not through the actual friends list for them to get the notification. Also the no cross-game voice chat is kind of annoying.
Your Nintendo Network ID with all your e-shop games is also system bound, so that can be bad if your system breaks or something.
My personal favorite games on it are Monster Hunter 3 : Ultimate, Sonic & All Stars: Racing Transformed, New Super Mario Bros. U and Nintendo Land is a good game to play with friends. The new Need For Speed game that came out last month also looks really good, I'll probably get it soon.
My favorite features on it are Miiverse and Off-Screen play, also just having the second screen in general is great for a lot of games.
Also try to ignore the doom and gloom people, all console launches start out rough