POP is U2's best album in my opinion. It still sounds fresh to me. The lyrics, the rhythm section, and the Edge's effects are like no other. What I love about it is that the product sounds greater than the parts and doesn't sound like U2 are trying to be U2. All the songs are different and unique, yet they form a cohesive whole. It's the only album I can listen to and not "see through" their motives. They created a sound that, if I remember correctly, Bono said was "not invented yet". It's also the only album where I don't prefer the live to the original recording. I love the production and feel of the album. It's got both an organic and otherworldly feel to it. And to me, it just sounds solid. I have respect of all of U2's music, but this album's got a heavy, solid feel to it that's not present on any other U2 album.
As for NLOTH, I really wanted to love it, but I couldn't. As some have said, MOS is a great song - the best on the album. When I first listened to it, I was into the first three songs, but then Unknown Caller and I'll Go Crazy killed the momentum. Boots was OK and I liked Stand Up, but Fez and White as Snow sounded like unfocused noise and a boring acoustic number, respectively. I liked Breathe and I the mood of Cedars. So I was so-so about the album. I really tried to love it, but it never happened. It's too disjointed.
I believe, though, that U2 can still be great. Edge needs to do some solos, Bono needs to sing about something important to him (hell, maybe he could even sing about wanting to be relevant and make it general enough to apply to anybody wanting to fit it), and the sound should be different.