I've been playing this since release. It's ridiculous how much fun this is.
As for mouse + keyboard: Splatoon actually has motion controls that work really well, it doesn't give you as much accuracy as m+kb but it gives you much more control over the game than a standard gamepad. Here's a video: https://www.youtube.com/watch?v=a3O65gi0MQc
I don't see the appeal but then I'm not into games like I used to be. It's nice to see Wii u is getting more attention cause it seems like there aren't many games for this console.