Rock Band Blitz is not a cover of Frequency or Amplitude
Yes, I'm surprised too. Rock Band Blitz, despite its superficial similarity to Harmonix's PS2 music games, Frequency and Amplitude, is fundamentally different from those -- and from Rock Band. Well, okay, you're still hitting buttons in time to music, represented by icons coming down the screen. It's not that far gone.
But almost everything else has been rethought. Instead of Rock Band's five "buttons" per instrument or Frequency's three, each instrument track in Blitz is limited to two tracks, with imported tracks converted algorithmically from the original Rock Band version. It is, technically, a simplification, but it's still challenging enough when you're juggling four or five instruments. And when you're playing Megadeth's "Symphony of Destruction."%Gallery-152627%
The challenge is the focus of most of the tweaking. There's just one difficulty setting now, and if that shocks you, you're going to pass out after this next sentence. You can't fail out of songs, and missing notes doesn't kill your score multiplier. Your score multiplier is basically additive only; every time you successfully complete a measure in an instrument, that particular instrument's multiplier goes up. Checkpoints in each song reset everything's multiplier.
This "leveling" system motivates you to jump from instrument to instrument, which is good because the "locking" mechanic from Frequency, Amplitude, and Rock Band Unplugged is also gone. In those games, a successful chain of notes caused that lane to "lock" for a while, with that instrument playing itself so you can jump to the next one. In Blitz, you can play the same instrument for the whole song if you want, and it's totally up to you when you want to jump over. There's some external stimulus since segments with more notes are going to get you more points, and you want to get every multiplier up as high as possible, but you actually don't have to pay attention to any of that if you don't want to. You can just play any instrument you feel like in whichever segment of the song is up.
The game is still about scores, this time adding a social layer of asynchronous competition by way of comparing scores with friends -- but at the same time the scoring mechanic doesn't dictate the way the whole game works. It's a more freeform experience, inasmuch as a game about being told exactly which button to press, and when, can be considered freeform. It's casual without being "casual." And as much as I don't want to admit it, that's actually more interesting than a return to Frequency.
