So for years and years, when discussing double-disc (typically 2 CD) albums, usually concept albums, a lot of fans will often say that the first disc/half is always better than the second disc/half, but why is that? A lot of folks might say that the artist felt like they were running out of steam or ideas, but I think more often than not, it has to do with the format and medium of the albums, and our perception of these long albums.
I think a lot of folks will say the first disc is better because when listening to said album, they'll typically start at the beginning (as you always do), and because of its length, you might not finish listening to the whole album that time, so you always revisit the first half more often than the second half, which might influence your opinions on the album. The more you listen to the first disc, the more you're likely to like it or absorb it enough to form a more solid opinion, while your lack of listening to the second half might lead you think the music isn't as good.
I think if all music for these long albums could fit on a single piece of media, there wouldn't be these discussions/arguments/debates about whether or not the 1st disc is better than the 2nd disc, because there only delineation between the songs would be specific songs themselves, and so fans would have to really pinpoint their least favorite/disliked songs on a long album, rather than just lumping the 2nd half together because the format of the album allows it.
For the most part, almost all of my music listening has been digital for years now, so listening to 2-disc albums is usually done in a single playlist, so I don't really hear/feel where the album splits unless the concept makes it very clear. Otherwise, these concept albums are given the full-album-feel for me, which allows me to really dig into the whole thing, rather than replaying the first disc over and over because I don't have to change discs to get through the album.
Now, I wonder if folks had the "which side of the album is better?" discussions for when vinyl was at its height in the mid-20th century. Or if the same debates happened with music switched to cassettes (side A vs. side B). As the medium upon which albums have been pressed on has gotten longer over the decades (up to 80 minutes on a standard CD now), albums themselves have gotten longer, and even some double albums in the days of vinyl now fit onto a single CD, like The Who's Tommy. For fans who only know Tommy as a CD and not a double vinyl, there probably wasn't any discussion or thought about "vinyl 1 vs vinyl 2", just the whole album on one CD.
Personally, this is probably one of the few upsides to listening to music digitally - you can get the whole thing in a single playlist without having to worry about changing discs or LPs midway through listening, so the experience can continue uninterrupted, which is good for rock operas/concept albums, especially where songs tend to segue into each other. I can guarantee if DT's Six Degrees Of Inner Turbulence had been released on a 100-minute CD, there wouldn't be all those discussions about "Disc 1 vs Disc 2", but I guess it's the nature of music fans to create debates wherever they can to fuel discussion or any sort.
-Marc.