It's probably Rivers' most personal album. And probably Weezer's best. It's rough, real, deep, meaningful and just all around amazing.
When it was first released, it was both a commercial and critical failure, and I can see why that would be. It's so completely different from their debut Weezer (also known as The Blue Album to fans). Its not powerpop, and its not straight forward musically. It flows.
It's also loosely based on the opera Madame Butterfly which is just freaking cool.
It's grown quite a following in the past few years, reaching gold in 2001, and coming out as a major influence on bands like Saves the Day.
The best way to explain this phenomenon, is by saying it was ADVANCED (see Chuck Klosterman's latest book IV pg. 249-254) when it came out.
Pinkerton is not only one of Weezer's best albums, but possibly one of the best ever written.
It might just be sneaking into my top 5.
Just go out and buy it.