It's so bad that even George Lucas hates it. The full two-hour special aired once in 1978, and never again. Lucas has blocked any attempt to get the Special shown again or released to home video or DVD. The only way in which it has survived is by numerous bootleg copies. And if you watch it you can see why.
I only made it 33 minutes in, and I can't believe I sat through it for THAT long. It's awful. It is notable, however, for being the first appearance of Boba Fett, as well as the first time we see the Wookiee home planet of Kashyyyk.