Huh, well, all I have to say is that I did not like KOTOR II as much as KOTOR I, simply because the story was not a of traditional movie-Star Wars style, or not as much as KOTOR I. Also, bugged up, likev everyone said, but that is expected (since it was also like this with the first one; at least I didn't experience any of the story-killing bugs).
I will expand upon this later. For now, bump.
The Good:
1.) Weapon switching, as mentioned (I don't remember clearly, but wasn't this part of KOTOR I, or not?); not so much because I had to switch weapons, but because it didn't look right for to be running around the city with a lightsaber-in-hand.
2.) More custom options/add-ons for weapons. Almost too much (especially with the droid components). Best, like mentioned, were the lightsaber options, not only the colors, but also the parts and the power crystals. Cyan, veridian, silver what not were cool, but maybe next game around they'll include a "variable color crystal" as an item, and you can set the color using a paint-style RGB spectrum.
3.) More power, Jedi rank classes, bonuses for perfectly dark or light alignments.
4.) Robes that flow. You don't know how important this is to a Star Wars themed game. KOTOR I had Jedi robes that 'clung' to the character's body, while KOTOR II solved this by adding a flowing tail. I believe they paid particular attention to this aspect.
The So-so stuff:
1.) Graphics. OK, I'm fine if KOTOR II used the same graphics engine as KOTOR I. I don't play this game for the graphics, and plus, KOTOR I didn't look that bad. But KOTOR II's graphics, particularly the distant horizon textures, dissappointed me. Compare Korriban from KOTOR I (the Valley of the Sith was beautiful, dispite low poly counts) to the dilapidated Korriban from KOTOR II (I know, its supposed to be, but look at the sky; that's a terrible texture). I'm reminded of Korriban and the Unknown Planet in KOTOR I the most, as the horizons looked like something modelled out of TerraGen.
2.) Lack of connection with NPC characters, and even the Exile character him/herself. None of the NPC sub-stories were nearly as developed as in KOTOR I. For instance, Bao-Dur has almost not sub-story at all. "Can I talk to you?" "Sure" "1.) Nevermind."
3.) Connections with KOTOR I were very, very limited. We get the droids, the most uninteresting characters from KOTOR I (IMHO) and a 30 second cameo of Bastila. Perhaps if a game would be made about the Exile after KOTOR II, that would be interesting.
I will continue this...
KOTOR II is by no means a bad game, KOTOR I was just better.