Surprised Kid icarus isn't mentioned yet. If you get passed the controls the game can be really fun and multiplayer can become a huge aspect of the game itself. Yea you can jump into online matches to have some fun or you can grind to craft the best weapons to tear people up in online modes. The game can work for casual or hardcore, the hard part is the controls.
Mario Kart, Kid Icarus, and Luigi's Mansion are the most fun, IMO
No, just no. LM is a trolls and idiots paradise. 70% of the people playing the game has no idea what to do and just stand around playing with the vacuum and using the "hellooo" feature. 20% is just trolls impeding your progress, 5% of people know what to do and are trying to play.
Voice chat would instantly fix most of those problems, but that's too much to expect isn't it.