So you picked up the Knights of the Old Republic II: The Sith Lords in the bundle that has just been released with the original Knights of the Old Republic for PC by LucasArts. You may be wondering why The Sith Lords feels unfinished. That's because it was. LucasArts had Obsidian rush the game to make a Christmas 2004 release. That meant they had to delete or truncate a lot of content that was meant for the game, including the ending. Obsidian reportedly requested that LucasArts release an official update to the game to restore the game to Obsidian's original vision, but LucasArts denied the request.
Luckily, Obsidian included the cut content in the game's data files, and fans have gone to work restoring it. There was a fan project called The Sith Lords Restoration Project, but that project was uncompleted and the team disbanded in 2010. The Sith Lords Restored Content Mod has been filling that void. The newest release, 1.8, was released a few days ago. This release fixes many of the bugs from the official release and adds all of the deleted content that The Sith Lords Restoration Project did, as well as the rest of the cut content that the former mod intended to incorporate (which is all of the deleted content with the exception of the cut planet M4-78). You can view the full list of content the mod includes here.