KOTOR2 is an ugly NWN2 mod with poorly designed locations, lightsabers that can't cut through anything, and a villain that looks like a cross between a transvestite nun and the Phantom of the Opera. It starts out bland and gets worse.
The Old Republic is a garbage setting. They took the setting of Star Wars, copied it, then replaced everything in it with pseudo-instances: pseudo-stormtroopers, pseudo-R2D2, pseudo-C3PO, pseudo-Millennium Falcon. It's supposed to be thousands of years before the events of the movies, but everything is exactly the same...except it has a slightly different name and looks a little bit different. It's a stunning example of low-effort marketing.
NWN2 d20 mechanics don't fit Star Wars at all, mainly because very little effort was made to adapt them - because d20 is supposed to work for anything, I guess. The d20 mechanics as expressed in NWN are pretty bad to begin with, and when you jam them into Star Wars without radical revision, they become nonsensical.
Dark Jedi Masters are trash mobs.
In KOTOR1 you had to work to become a Jedi, but in KOTOR2 you start as a Jedi, and all your stupid companions can become Jedi Knights, no matter how emotionally unstable and unworthy they are. All it takes is some sweet talking and a cutscene. Everyone is a winner!
In Star Wars movies, the pattern is to shift from an artificial location, to an organic location, to a new artificial location, to a new and radically different organic location. For example, you have a battle on Princess Leia's ship, followed by an adventure in the deserts on Tatooine, followed by a battle in space and an adventure on a space station, followed by a landing on Yavin 4. KOTOR2 violates this by moving you from ugly man-made Peragus to ugly man-made location number 2 to ugly man-made location number 3. Even KOTOR1 did this better than KOTOR2.
The writing isn't nearly as good as it's reputation, and it if weren't for Kreia's excellent voice-acting, it would be held in much lower regard. On the whole, it's a pretentious, ham-fisted attempt to combine Sith philosopy with Friedrich Nietzsche. Beyond that, the actual events of the game make very little logical sense.
HK-47 was the lone bright spot from KOTOR1, so in KOTOR2 they tried to make more of him, but even that's a failure. It's a hollow echo, like someone trying to write jokes "in the style of" a successful comedian.
If you absolutely must play a Star Wars game, play Star Wars: Jedi Academy instead. At least the lightsaber fights are fun.