They are all albums, and all have their own personality.
Whilst some albums are stronger than others, they all represent a time in place for U2's career.
The compelation cd's & b-side cd's are the collection of songs, when you have grown up with each and every one of U2's albums, you take them, digest them, listen over & over again, i just cannot see how they are just a collection of songs.
Agree with Stu. Some of them have more of an "albumesque" flow then other albums. But they still all sound like albums to me, especially compared to some of the "albums" that other bands put out there