One word, Portable .
I hope this helps. To start the game is immersive. You are a band so form one, pick your appearance, start in small spots and as you progress bigger opportunities will open up, and you'll attract more interest. The songs might get harder, but at least you will unlock more songs.
The songs are great, if you search on the net somewhere and see the track listings you will know if you like or dislike them. But most are platinum hits, and have worldwide audience. They also fit the game really well. But I understand if you do not like the music, we are all individuals, and unfortunately you will not get the opportunity to upload your own songs, although DLC is available at a price.
The game kept me busy, I am a pretty laid back person and liked the game because it had a point, but was not forcing some issue down my throat. It was music, a PSP and my button pushing skills. With practice you will improve. To be honest I was never really impressed with the full set up rock band instruments, having your friends over, and play songs but this portable version really is awesome.
Its a guilty pleasure for some, but the graphics and sound are great, the gameplay is easy and sort of a classic.