There's little question that the four-disc box set Long Train Runnin' 1971-2000 is only for hardcore Doobie Brothers fans, since it not only spans 79 tracks, but it also contains a full disc of rarities. The sheer abundance of material makes it unnecessary for anyone that isn't already a dedicated fan, either of the Doobies or of album rock, and even those listeners may find Long Train Runnin' a little long. After all, the Doobies' hit-making years end around the end of disc two, even though a few hits spill over to the beginning of disc three. That means the first half of the box is essentially an expanded greatest hits, featuring all the '70s singles -- from "Listen to the Music" to "Dependin' on You" -- balanced by a handful of album tracks. There is some elaboration of these years on disc four, but it takes a while to get there, since disc three chronicles the '80s and beyond. In the early '80s, the Doobies had only one Top Ten hit with "Real Love" before going on hiatus. They reunited in 1989 and continued to tour and record throughout the '90s. Those two decades comprise disc three and while it has its moments, it pales considerably next to the Doobies' prime material. The rarities disc is similarly uneven, but more interesting because much of the music dates from the '70s. Also, the mix of solo songs, alternate mixes, and demos illuminates those classic years somewhat, throwing out a handful of gems along the way. It's a nice bonus for the dedicated, but they really are the only audience for this set.