I don't have access to too many rhythm games because lack of time/funds, but on the ones that I have played, this is probably my skill level.
Taiko no Tatsujin: 5 Muzukashii, no Oni why :<
IIDX: 5 (really not that good)
DDR: 10-11
Project Diva: I can usually FC all Hards, and can Excellent some of the easier Experts. My thumbs aren't super co-ordinated.
osu!STD: Can FC 4*, can usually beat 6*.
osu!Taiko: Can FC 2.5*, can usually beat 3.5*.
osu!CTB: Used to be much better...can FC 2*, can beat 4*.
osu!mania: Depends on keys really, 4K I can FC 2.7*, beat 3.7*. 7K, I can FC 2.5*, beat 3*. All other I dunno because lack of those beatmaps.
Yeah, osu! kinda dominates the list, but like I said, I don't have access to too many rhythm games.