Its Green Day...its Rock Band...and its very good.
But, if you like Green Day, and if you like Rock Band or Guitar Hero, this is almost a must purchase for you. The game is very much like The Beatles RB, but it does not feel as cinematic and there is something that is just missing. Its hard to explain, but The Beatles had a certain something about it that is not as present here. Green Day's into sequence is cool, but not as psychediic or unique as the one we saw in The Beatles. But, the music is great and you will find that many Green Day songs are more fun to play, and just seem better suited for a RB game than many of The Beatles songs. I forgot just how good an album Dookie was. Yes, there are songs missing and Insomniac is woefully underrepresented. I also do not get how nothing from Kerplunk or 1039 Smoothed Out Slappy Hours made it on here due to something Mike Dirnt was saying about the analog nature of the original recordings (your telling me The Beatles had better equipment in 1965?) But, the songs that did make it on are all top notch and you will greatly enjoy songs like Longview, American Idiot, and Murder City, along with many others.
All in all, Green day Rock Band is infinitely better than GH Aerosmith or GH Van Halen and it's every bit as good as GH Metallica. I would put it a notch below The Beatles RB, but it still gets an 8 of 10 in my book. I suspect we are going to see some pretty good DLC down the line and I would be stunned if Kerplunk is not a full download one day. I also think we may see a cameo from the Foxboro Hottubs somewhere down the line (maybe The Network as well). If you like Green Day and you like Rock Band, this is a safe purchase and a great game to add to your library.