WWWAAAAAYYY TOO FUN!!
Guitar/Bass: The guitar/bass in the game is by far the easiest instrument to play out of the three. The guitar/bass is also the most played instrument because of Guitar Hero, so many people are already good at guitar (including myself :) ). The solo tour in the game is fun for all difficulties and for people who overplayed Guitar Hero (including myself again :( ) is a very refreshing 58 songs to play on guitar. The guitar that rock band comes with, has 5 normal buttons and 5 "solo" buttons that are at the bottom of the neck. These buttons are incredibly hard to use because of they're size and the fact that people who play expert don't want to go down to medium just to play the solo buttons ( in other words the solo buttons are pretty much useless on expert). On the other hand if you are just starting out on the rock band guitar and work your way up it is very possible to be very good at solo buttons. The guitar itself is phenomenal! From the non-clicking strum bar (YAY) to the whammy bar to the thing that changes tones (I don't know what it's called) everything is good about this guitar.
Drums: The new instrument. Drums is the funnest instrument in the game because it's new, challenging, and the fact its drums. Not to say this instrument is easy though. With drums you usually have the talent or you don't. If you don't you play easy or medium if you do you play hard and work up to expert. The kick pedal on the drums is the hardest part of the instrument. If you've played it you know what I mean if you haven't then let me explain. The combination of the kick pedal and the pads and the sometimes insane patterns to follow will almost always throw you off a couple times. Drums on solo tour is fun... but be prepared to stop at the 7th group and get a beating. For some weird/insane/stupid reason they put the longest and hardest song (AKA Green Grass and High Tides) in the 7th of 10 groups of songs. Other than slight problems with drums not picking up the odd beat, I tip my hat for Harmonix.
Microphone: Not for karaoke. The microphone idea has been used in other games (Singstar...) and is mostly the same. Unfortunately there isn't much you can do with a microphone but trust Harmonix to figure something out. Other than the classic "try and hit the pitch" of microphone there is also a part in some songs where you have to tap the microphone. On the screen the singer will pull out a cowbell or a tambourine and... Well I'm sure you can figure it out. The microphone is surprisingly accurate and incredibly fun to piss people off with.
Generally: Altogether this game has dump truck loads of fun in it. The multiplayer is awesome, and the 4 different difficulties make this game fun for anyone. There are 58 tracks full of classic rock, new rock and everything in between. On the downside, the ps2 version is stripped of online, the character customization and downloadable tracks. This is not a game for hardcore gamers because it is really short and fairly easy for the difficulty that the person can play without failing. On some other downsides: Fallout Boy, no ACDC, Led Zeppelin, or Pink Floyd (Man they need to get the rights for them) and lastly an Aerosmith song NOONE HAS EVER HEARD OF!!
A TIP FOR THE WISE: THE INSTRUMENTS ARE DURABLE BUT WILL NOT STAND UP TO ABUSE. IF YOU WANT 3 WORKING INSTRUMENTS FOR A LONG TIME DO NOT ABUSE THEM.