Don't be fooled by buzz words like keyboards and Pro Mode, because this DS version isn't anything new.
Rock Band 3 for Nintendo DS features most of the same additions as the home console versions. You've got your keyboards, your Pro Mode, and your "Bohemian Rhapsody." Unfortunately (or maybe fortunately), you get all these features without any peripherals for your DS. It's a great game nonetheless, but it's more for the people who love Amplitude and Frequency than the folks who want to rock out to "Cold As Ice" by Foreigner.
The game features the typical four-lane note highways that the Rock Band series is known for, but instead of strumming along you press buttons at the right time. It's a simple mechanic, but it's addictive and entertaining, especially since the button presses match the beat of the music.
There are four note highways on the screen, and you have to switch between them to play different instruments. Only four instruments can play on a song at one time, meaning that keyboards are switched in and out with another instrument depending on the song selected.
The regular difficulty settings task you with successfully playing phrases, which are sections of music that split the song up on the highway, for each instrument. After you complete a phrase, the instrument will play itself for a while. If you're good, you'll be jumping from instrument to instrument and never miss a note. Along the way, you also have to keep up your multiplier, which of course goes all the way up to 11.
Pro Mode's main difference is that you have to keep up each instrument constantly; there is no break during which any instruments play themselves. It's a challenge, and requires players to employ a slightly different strategy to perform well. It should be noted that this type of Pro Mode originated in Rock Band Unplugged for PSP, which featured a similar mode.
The DS version only features 26 songs, which is only a mere slice of the full Rock Band 3 set list. There's a bunch of cooperative and competitive multiplayer features that look fun, but since they all require multiple copies of the game, the likelihood that people will ever experience them is slim.
Rock Band 3 for DS isn't the revolution that the home console version is, but it's still a fun rhythm game in its own right. If you love games like Amplitude and Frequency, then check this game out.