Don't get me wrong, I love Avellone. He gave me some of my favorite games. But he failed on TSL. LucasArts screwed up, too, but Obsidian is not entirely innocent. NWN 2 also had the rushed ending of TSL.
Also, they made the actual Sith Lords really lame. Sion falls in love with the Exile? Nihilus never even speaks a recognizable language? Kreia was okay, but she really was mostly just the typical Total Nihilist you see in every other fantasy or Sci-Fi. "Blow up the Force". What the hell?