Been there done that.

User Rating: 6 | Ultimate Band DS
First Impression:
Looks decent. I like the idea. OOH! CUSTOMIZABLE AVATAR!

Gameplay:
So the first thing that reeled me in was the idea that you could customize your avatar and use it to play through the game like you would with an actual band.
Er...
No you can't.
You get to choose from a set of predesigned avatars and then you get thrown onto a map of sorts. On that map are clickable locations that get unlocked and give you new songs. There's also a recording studio where you can make your own songs by playing the instruments like you usually do during a gig.
You get three types of guitars (Lead, Bass and Rhythm) and a set of drums to play during the gigs. Lead and Bass are played by tapping the notes when they get to the pickup area and holding down a directional button along with the tapping when needed. The Rhythm guitar is played by strumming (IE, dragging the stylus across the strings) and holding down a directional button when prompted. The drums are no brainer: tap the note when it approaches the drum.
Every gig has three songs unlocked which get added to your repertoire. With each location is a bar you fill. When the bar is filled, you pass the location and unlock a new one as well as three more songs.
Of course, the deeper you get into the game, the longer it takes to fill the bar. Playing the entire list of songs you've unlocked can get quite tedious and changing the mode to hard doesn't help alleviate the tension.

Response wise, everything seems fine save for the Rhythm guitar. At times, it can't read your strum.

Last words:
I was hoping for customization and was disappointed. I was looking for something more fun and strum worthy but alas, that too was taken from me.
Maybe you might like it. I don't. Not too much. I'd rather play Taiko Drum Master.