Anyways, about the actual game itself. KOTOR 2 is a very good game. To compare it with KOTOR 1, KOTOR 1 was a very Star Wars-y game. It had the interesting setting, fleshed out characters, entertaining and sometimes moving writing, an epic feel of a galaxy being at war, the jaw-dropping plot twist that changes everything, etc. It did a lot to capture the feel of the original Star Wars film trilogy (arguably better than the prequel film trilogy did). All in all, a fantastic piece of gaming entertainment.
KOTOR 2, on the other hand, is almost not a Star Wars game. The general feel of the game is more moody and thoughtful. It's a darker take on the concepts of the Force, Jedi, and Sith, and you as the main character get more development. One could say that the thematic core of KOTOR 2 is much stronger than KOTOR 1. It's a bit more low-key, as instead of the grand war against the Sith taking place there's a secret war with the Sith quietly persecuting the Jedi to extinction. On paper it's every bit as good as KOTOR 1, and in some ways even better.
The problem though is that KOTOR 2 was infamously rushed by LucasArts and Obsidian Entertainment, the developer, had to cut a bunch of content. Most specifically the ending feels a bit too sudden and barebones -- not that it's a bad ending with regards to the story and writing *coughMassEffect3cough* it just had a bunch of its content stripped to meet the deadline. Over the years fans have been working on mods to restore the content, and a full restoration mod is now available. If you're going to play the game I would highly recommend using the mod.