Sorry to double-post, but I wanted to express something:
The more I play other rhythm games the more I realize what I like so much about Bit.Trip, Sequence and Rock Band.
Not only do they sync to the music well, but I was always able to pick out what I'm supposed to be listening for. In Rock Band it's partially because you only play one instrument at a time. But there's more to it then that. In the best Rock Band songs and in the entirety of Sequence and Bit.Trip.Beat I felt like the mapping of music to mechanics was done with a great deal of intelligence. In a lot of otherwise fine rhythm games, I find that the choice of which notes to make mechanically enforced and which notes to add with higher difficulties ends up feeling off to the point that sometimes groking the song can hinder as much as help.
This isn't necessarily a bad thing--the game can still be an interesting challenge when this happens. I have to puzzle out what line these notes are. What rhythm IS that? What subdivision is that supposed to be? What instrument do I follow here? Have we switched to drum lines? Ah, yes we have ... but somehow the three games I mentioned above get rid of most of the guess work. In the case of Sequence and Bit.Trip, it's all about flow because the rest feels so natural.
To use a specific game: fairly frequently in Osu! I'll feel punished not only for being awful at the game (I'm really awful at it) but also for reading the music differently than the beatmap does and expecting different things--and some of the time I think the beatmap is not just different but at fault. That's an experience I never have with Bit.Trip or Sequence and both games seem to achieve this in different ways. In Rock Band it was far less common--probably because it's a high enough budget game that there was a lot of editing of the songs and even of the automated tools. The difficulty scaling felt really weird and awful in older Rock Band World Tour (the only other one I've palyed) but really solid in Rock Band III.
Just what I'm thinking as I go through a bunch of these.