Even most of the best hippie/prog albums are fortysome minutes long because the LP format pretty much forced them to. Goddamn digital. I feel like I have a pretty awesome attention span, but rarely can I ever become completely engrossed by a long album (there are a few exceptions). It was also cool back when bands released a new album every ten months, with plenty of singles in between.
I agree mostly. I used to think the more the better, but now I can also feel this intangible "fence" beyond which plenty becomes too much, and detrimental to an album's overall impression, regardless of quality. It's a different story with concept albums that actually manage to justify the overtime. Many do not.
Perfect example: The Lamb Lies Down On Broadway. Cut that thing down to 50 minutes and you have the best album of their career. The same could probably be said of Tommy, The Wall, etc. I can only think of a couple long albums that COULD NOT be trimmed without taking something away: Lift Yr. Skinny Dicks, Bath/LYBM and The White Album.
Kerbenok's O is 71 minutes but feels like 45 as not a second could be left out. I guess it's only about that: quality. As erik put out, even an album with 40 minutes of absolute 5-stars awesomeness becomes slightly annoying with 3-4 aditional fillers.
Judas Priest - Painkiller 46:10
Iron Maiden - Seventh son of a seventh Son 44:06
Dissection - Storm of the light's bane 43:16
Amon Amarth - Once sent from the golden hall 44:51
Dark Tranquillity - The Gallery 47:49
Candlemass - Nightfall 46:35
Iced Earth - Night of the stormrider 46:05