I remember when it was good, but I don't really remember a time that there wasn't a fanatical vibe to it. The content there has always been strongly pro-Linux and anti-Microsoft. There was a time where people actually used the phrase, "Year of the Linux Desktop" without being sarcastic. Oh and writing "Micro$oft" was popular too. And there was always stuff about open source and GNU and GPL and etc.
The thing that made it good was the camaraderie, the general helpfulness, and the quality of posters. You used to be able to find some really intelligent content in the Slashdot comments, since some the smartest people related to that particular topic were probably Slashdot users themselves.