Tortoise is credited with helping to usher in the genre of Post-Rock, along with Mogwai. Their 90's releases garnered a good bit of praise from critics and fans of eclectic rock music everywhere. Millions Now Living Will Never Die (1996) and TNT (1998) represent groundbreaking forays into more jazz influenced compositions and experimental production techniques that were heard rarely in standard radio rock. The track length of some of their songs is intimidating, and sometimes frustrating (it's much harder to find a specific movement within a song than it is to find a certain track on an album), but it's by no means a dealbreaker.
From Millions Now Living Will Never Die (1996)
From It's All Around You (2004)