Green Day has run into the problem many bands have faced - how do you make a career out of something inflammatory?
No one cares that Barry Manilow put out various types of pop schmaltz for decades, because that's about all he ever put out, and neither he nor his fans wanted/expected anything more. With him, "edgy" meant recording "Copacabana" or "Some Kind of Friend", neither of which would stun a standard fan.
But punk (and pop-punk), like rock-and-roll (circa 1956) before it, was loud and shocking to the masses. What do you do once everybody's watching, and they're expecting you to be loud and shocking? You can fulfill those expectations, at which point you're getting kinda stale. Or you can try ramping it up further, although chances are you didn't keep much in reserve your first few go rounds. Or you can take a detour, and risk alienating your fanbase.
Green Day has sort of tried all of the above at various times, to varying degrees of success. They've tried staying the course (Insomniac, Warning), and they sounded fine if overly familiar doing that. They tried ramping it up, which in a sense was what American Idiot was all about. And they succeeded there, in my book, although the follow-up seemed more labored than normal. And they've tried detouring. "Time of Your Life (Good Riddance)" was almost shocking the first time I heard it. The Foxboro Hot Tubs was a really fun detour through classic punk/garage/60s rock. And the musical was an interesting idea but one that didn't work in my eyes.
But they're Green Day. This type of music, to whatever degree, is what they do. What should they do - give up? It's not like their new material is awful, or even bad - it just isn't as fresh as one would hope. They're still making good music - they're just no longer the new faces on the scene. And after two decades of putting out music, one can forgive them for sounding "craftsman-like" or "journeyman".
The fact is - it's always been thus. Show me a musical act that has been around for decades, and I'll show you one who put out substandard albums of typical fare, passable-to-terrible musical detours, or both. The true joy is seeing them suddenly rediscover their muse, or tap into something just right, and see them produce great music once again. And that can be anything from Paul McCartney's "Run Devil Run" (and most of what followed) to ZZ Top's "Eliminator" to Elvis's "Suspicious Minds".
Lex