I think their music is overlooked a lot because of Bono's good-old-fashioned-boy image and the sometimes cheesy stuff (even Bono's voice is cheesy as hell). And they've been clearly repeating themselves sonically in the 2000s.
They haven't always been like that. In the 90s they experimented a lot more with music:
Has Adam Levine's singing voice always been so whiney? I remember when Maroon 5 debuted, he didn't sound as whiney as he does on "Payphone" (even tho I love the song). Or does it just vary from song? I've only heard their singles.