This often coined musical phrase always make me think of a certain album (but no one was interested in The Damned thread, probably showing my age there).
Truth is 'most' 2nd albums are great (if you like the artist in the first place of course). The Clash, The Damned, Ramones, Dead Kennedys, Fugazi, Nirvana, Electric Wizard, Black Sabbath, Radiohead, Boards Of Canada, The Cure, The Cult, New Model Army, Danzig, Joanna Newsome, Beastie Boys, Public Enemy, Butthole Surfers, The Cramps, The Specials..... many, many more. Some of these artists namechecked even surpass great debuts with their 2nd album - which raises the question why the phrase exists anyway? Struggling to think of an artist / band that have a 'difficult 2nd album' - Guns N' Roses maybe? More?