Y'know, when the name of the game is breaking your keyboard/controller to the beat. The few that I mainly mess with are Clone Hero, osu, and Cytus II.
Clone Hero: a clone of Guitar Hero 3 that runs on PC and allows the play of customs. I mainly just consume content and create a couple of charts here and there for when I make a custom of my own. That'll have to wait 'till at least December.
I did get my hands on a Bluetooth keyboard, which is easier to use in terms of pressing the keys, but its poll rate is atrocious. Only a stopgap for an actual plastic guitar. I've got an actual Les Paul Wiitar now (with a Raphnet adapter)! Check out my ScoreSpy profile here!
osu!: mash your mouse/pen and keyboard to the beat. I've only racked up about 10 hours total, so I'm no good. Only played enough to get the hang of it and be able to not embarass myself in front of the lads. I occasionally play it for fun on my own accord, but only rarely. I'm too busy to make it a habit or anything. Check out my profile here!
Cytus II: a mobile rhythm game with a built-in storyline. I mean, I guess I'm good at it, but I haven't completed the entire story yet. No spoilers if you know how it ends!
I might get into Dynamix, which is another mobile rhythm game, but first I'll need to gauge whether I have enough time and energy to take that on.