The first crash for me was shortly after they got married, right before Electric Superman. Nothing in particular I can think of as far as why I stopped reading, I just didn't care that much anymore (combined with moving to an area without a shop in good proximity). Hopped back on around 2004-ish and bought trades of the more important arcs like President Lex, as well as collecting monthlies again. This lasted right up until New Krypton, which killed it for me once again for that whole year. I bought Cornell's Action issues, though.
Looking at Post Crisis Supermans timeline of stories overall, I'd say a graph of its quality would probably resemble a roller coaster. The really good parts didn't last more than a year or two, but the really lame stuff didn't last for more than a couple years as well.