I agree, Hi-Fi was better than the last couple releases before it. For my ears on the REM offerings, how goes Peter Buck, so goes the band. If he gets apathetic or stuck in the same rut for an entire album, sound-wise and attack wise, it's hard for the rest of the album to rise above that.
I still miss the jangly meandering Peter Buck style of old, not to mention the dueling, interwoven countermelodies of the two Mikes, but I don't fault them for growing beyond that.