Arms is really great! Its easy to play but takes a bit to master. You can get way in depth into it and play ranked and really have a great challenging fighting experience. Or just mess around in party mode, one punch mode, or even with random arms. It has a lot of modes and different options where you can just mess around and have a lot of fun. it's really reminiscent of old-school 64 Smash Bros that way, but since this is a modern game, could probably use a little more content or modes, but it is the first of a new series so I don't expect it to be as flushed out (content wise) like the long running titles such as Tekken and street fighter. I would buy it again and it keeps getting better.
If your one who loved playing through smash bros with each character, then you can easily spend so much time on single player. I wish there was a more story heavy mode and the GP be the career mode, but they have added one mode since launch. Otherwise online multiplayer is where this game truly shines.
Controls are great with both motion and standard, though they have their pros and cons (pun intended) but they just added button mapping and sensitivity for motion controls and a lot of the problems are gone.