Great game, targeted for multiplayer.
To start of, if you are not familiar with how this games work, notes come down from a bridge and when they reach a point you respectively strike (or hit or sing) the right note. You continue doing this for all the songs until the end. There are 4 types of difficulties, from a slow pace beginning mode, to a very fast higher demanding mode.
I've recently got Rockband, and it is amazingly fun, with a lot of songs (50-60 not including the extras) in a wide variety from 60's music to current music. Also, great multiplayer ability seeing how up to 4 people can play either locally or online. It also allows you (and demands) to create a character.
The game comes with a drum set, a fender style guitar and a mic for doing karaoke. To link all this together it also comes with a USB Hub.
BASICS
The guitar in Rockband does not change from GH except you get solos, aside from that it still is the same. You hit the notes, use your star power (now called overdrive) and whammy to get extra points. What does change and add to the game are the new instruments which are:
-The Drums: Are basically 4 pads and a pedal. The pedal is interesting because instead of being notes coming down its normally a bar in the measure which you have to strike with your feet. It really gets you moving since its nonstop moving of arms and feet. Normally a lot of fun but requires a lot of beat, and it tends to be really repetitive in some songs (but quite challenging none the less).
-The Mic for singing: Which is basically karaoke. If you are not familiar with singing, or you've never tried it, you will come to realize how much you probably suck! Smile However, it still is a lot of fun. The lyrics come down below a bar, and a bar it self is shown to tell the singer what pitch to sing it at. Also at the receiving end (where you normally strike, in this case sing) there is an arrow which tells you at which pitching you are singing. Something nice about this incorporation is that it allows you to see how far you are from hitting the notes and in case you can not hit the notes because they are too high or too low, you can sing them by octaves.
STORY LINE
The game has an interesting "campaign" or story line. One can choose to solo the game playing one instrument or play in a band (which you must create). No matter which one you choose, the point is to beat the songs and unlock more songs/stages/items/locations. As you proceed through the game the songs get more challenging as well as more unlockables become available ranging from clothing to instruments to songs.
Soloing: In the solo mode you can create a character and choose an instrument for that character (this character can only play one instrument, except for guitar, since guitar and bass are consider the same in this game). The point is to unlock more items, go through, acquire money and ultimately beat all the songs.
Multiplayer: This mode has a twist. The point of this mode is also to unlock all items and beat the songs, but also to collect fans and sign record deals with companies. To do this, the whole group must play well and synchronized in order to get higher scores.
MISC
Basically, this game is meant to enjoy with friends. Not really designed for solo play, but either way you choose it is very enjoyable. There is also a mode called tug-o-war where you play head to head against someone to see who is better, but there really isn't much there except for bragging rights.
There is also small animations just like in GH while playing, but one rarely pays attention because the more challenging it gets the harder it is to look away from the notes.