Think about it. They dropped Absolutego in 1996, already an amazing stoner/doom metal record that would've been a career highlight for any other band, then continued on to eclipse it with Amplifier Worship (1998) and Akuma no Uta (2003). And lest you think they could only perform long-form stoner music, they're also responsible for Heavy Rocks (2002) and Pink (2005)--two of the best psychedelic rock records ever recorded. And then they threw in Smile (2008) just for good measure.
But no, Boris are no one-trick-pony. During this time, they also released some of the best post-metal and drone albums of all time. This includes the minimalist classic Flood (2000), their collaboration with SunnO))) Altar (2006), the sublime Dronevil (2005), and what is currently ranked as both the best post-metal and drone metal record of all time on RYM, Feedbacker (2003).
And in between releasing literally ten world-class works of rock and metal history, they also found time to release numerous other collaborations and studio albums just because no one was able to stop them. Stuff like Megatone (with Merzbow, 2002), the "Mabuta no ura" soundtrack (2005), the Thing Which Solomon Overlooked trilogy (2004-6), Vein (2006), and even more that I can't fricken remember right now.
No discredit or shame to their later work, but genuinely--I defy you to find me a better decade-long run of any band, ever. It's just mind-boggling to consider the incredible body of work this trio created in such a short span of time.