Just like The Beatles: Rock Band you can head online to play head-to-head or in a band. This is all pretty much as standard as pressing the first fret button to play a green note. Not much has changed here, just the music. For a large group of people, they are going to have a hard time dropping $60 on essentially one album they like (Dookie) and not much else (the rest).
Unlike The Beatles: Rock Band, you can export the songs to play in Rock Band 2 (and the upcoming Rock Band 3), but this time it will cost you $10. People who pick up the "Plus" version of the game get a token to export the songs, so this more expensive version of the game may be worth it if you are a big fan of 21st Century Breakdown, and having the tunes available in other Rock Band games.
Thankfully the difficulty of the game is harder than The Beatles: Rock Band, more in line with Rock Band 2. Dookie has some great bass parts that are fun to play, Your enjoyment is going to come from the overall music though, as the core game has been polished to a shine by now.
If you have been waiting to play Green Day in Rock Band, this is a game for you. If you only enjoy the "old" days of Dookie, the rest might not make it worth it. It might not be what we expected as a follow up to the The Beatles: Rock Band, but Green Day has an impressive catalog of music in their own right, and Green Day: Rock Band includes pretty much every one of their songs you would want to play.
Green Day: Rock Band is rated T (Teen) by the ESRB for Drug Reference, Lyrics, Mild Blood. This game can also be found on: PS3, Wii. Green Day: Rock Band Plus is also available.