Yeah, for real. Good News for People Who Love Bad News is a pretty awesome record, but it just doesn't possess that same vibe as old Modest Mouse records do. Isaac Brock sobering up might have something to do with it, as well as the addition of Johnny Marr.
Isaac Brock has been sober since right after TMAA. He wasn't on drugs for Sharpen Your Teeth, GNFPWLBN or WWDBTSES, but he did get pretty shitfaced in the early hours of the morning for writing a lot of the material.
Debate this if you want, but the sound changed because of major label control and influence. TMAA had some strange production choices, probably on the label's part, and they asked the band to write a pop song for the album.
The decision to add rhythm guitar on GNFPWLBN was a major label one. The label asked for some obvious singles on that album. The label chose to super produce it. That last album was the next logical step. That said, Johnny Marr joined the band because Isaac Brock really loves the Smiths and Marr hasn't done anything worthwhile since then. He doesn't want to admit it, but this 'hip' and 'new' band was a huge opportunity for Johnny Marr.
Isaac Brock can still write an interesting song. Unfortunately, for the band Modest Mouse, music is a business. It's their career. The way I see it, once your music becomes 'work', it's gonna show in your records, and I can't think of a better example of this than Modest Mouse right now.