If you loved Uprising but can't get into any of their recent lyrics, it's possible you might have just changed somewhat as a person from when you first got into that song. Matt can write some great lyrics, but most of us wouldn't point to that one as an example of it.
Mostly he's great at conveying emotion in some relatively basic statements. He sings the hell out things like "When will this loneliness be over," "I want you now," "Why can't we start it over again?" and so on, all of which are hugely common human thoughts and emotions, which is why so many of us love those songs. Very rarely he'll take it one step further and actually throw in some clever turn of phrase in there and we'll latch on to it to defend his lesser moments (looking at that one Hoodoo line everyone throws out when this argument comes up), but for the most part its very raw emotional lines that work best for him. And no, that doesn't make him Julian Casablancas, but there is still something to be said for that ability.
But if you've never cared for that aspect of his lyrics, then I'm not sure how you can be too disappointed with where they are now. Mercy really isn't significantly worse than Uprising in that sense. Hell, Animals is way better as far as that theme goes, in my opinion! But yes, overall the lyrics have gotten much worse and very quickly. I don't think it's because he just can't do better though. He just seems less interested or inspired to write those kinds of things we loved from the earlier albums.
If anything it's a bit more bleak for those of us who loves those earlier, "whiny" songs. If you love the political anthems, I'd stick around for the next album. One would think they can only go back up in overall quality after Drones.