Post-Nothing opened with anti-Thin Lizzy jam "The Boys are Leaving Town," which encapsulated everything this band was about at the time: growing up, leaving home, being unsure and nervous about literally everything now that they are on their own. The great thing about that record was that these themes were represented in the lyrics AND the music. They were these messy pieces that truly sounded like some young guys jamming out in a garage. Everything felt spontaneous, and that stream-of-consciousness mentality made the band/album appear brutally honest and therefore, earnest. I believe Post-Nothing is a wonderful album; it captures the late-teen angst (hate that word, but it sorta fits) that tons of guys go through. And that sounds corny on paper, but when listening to the album, the last word you would ever think is "corny."
Unfortunately, they took almost a complete 180 with the second album. Maybe the lyricism stayed, but the music/production definitely changed for the worse. Like f0rk said, it's over engineered. Everything here was pre-meditated and calculated beforehand. Rock is all about spontaneity. With this album, they completely got rid of the spontaneity, and then had the nerve to call it "Celebration Rock." LP2 felt manufactured, especially in light of their debut, which was so so passionate.
And it's totally fine if people like LP2. I was just dissatisfied with the route the band took.