I think Green Day have always been more than just catchy guitar riffs and lyrics. Their lyrics have always had a sense of humour about them but they've also always had serious themes. Billie writes honestly about what he sees around him and as he's got older that's natutally come to include more of the world, and religion and politics are part of that. If an album contains lyrics about those things that doesn't make it a concept album - a concept album is an album all about one really specific subject or that tells a story. He was touching on religion in One Of My Lies, and on racism in Road To Acceptance, on the state of society on Warning. And there's some pretty catchy guitar riffs on AI and 21st CB, not to mention Stop Drop And Roll.......it's not as simple as one minute they were fun and catchy and the next serious.
Seems like the direction they're going in might be a more simple rock and roll one this time but I don't see that as going back. They're not gonna go backwards, it's a new and fresh sound. Billie will continue to write lyrics about whatever he's compelled to write about, and since he's nearly forty that's likely to continue to include a wider view of the world than just his own life and relationships.