The first KOTOR was, in my opinion, one of the greatest games ever. Though it had its flaws, they were few and far between. Obsidian and everyone involved with putting out KOTOR 2: TSL deserves an enthusiastic round of applause for their efforts to make a follow-up to such a stellar game. They managed to come up with a sequel that, while plauged with bugs and other issues, is nonetheless relatively enjoyable.
First, the good stuff:
TSL is fun to play--most of the time--and delivers much the same kind of experience as the first KOTOR (after all, what can compare to barbequing hordes of Sith with Force Storm whilst laughing maniaclly to yourself?). KOTOR 1 was good, and TSL tries to continue in the same tradition. Though there are plenty of problems with the game (see below), it is worth the time, to play through a few times. Many of the new features, like the streamlined weapon-change function, or the "Empty" label for looted containers, or the fact that new datapads are automatically opened to be read, are small but very helpful add-ons. The new prestige classes add a lot to the experience, giving much additional replay value. The companion influence system is interesting, if a bit stifling at times. Aside from the gameplay, I feel compelled to praise the new Jedi/Sith robes in the game: unlike KOTOR 1, TSL boasts about four different, full-length types of robe, with probably two dozen different color schemes/stats/features--it is most gratifying to walk around in a flowing robe, something very Star Wars-ish that the first game just didn't convey despite the brilliance of everything else. The music is quite good, as is the feature on the main menu that enables you to listen to the different songs you've unlocked in the game.
Now the not so good . . .
The one word that comes to mind when playing TSL is "Potential." This game had *enormous* potential to be utterly amazing, but unfortunately . . . it's not. I've seen other reviewers griping about Lucasarts pushing Obsidian too hard, about the game not being completely finished when released, etc. I'm not going to get involved in all that, but there are a great many things that disappoint in TSL, and it looks like TSL was indeed *not* entirely done when released (Pardon me while I sigh miserably over the lost content).
The incomplete state of the game is the biggest issue for me. This means that there are vexing holes in the story--especially near the end, where, as I think someone else pointed out, the little tidbits of info on the load/save screens are more informative as to what's going on than the game itself. The first KOTOR really delivered a strong, continuous main plot that kept you riveted till the very end; TSL pales in comparison. The story is *there*, you can sense it, but it was not fully brought out and clearly delineated--again, wonderful potential, but it falls flat. The end of the game is nice, to be sure, but KOTOR 1's was, simply put, totally cool, and made your adventure worth playing. In TSL, well, it's more than a little disappointing.
The NPCs you find seem sadly, madeningly dull compared to the first KOTOR. They don't have nearly as satisfying backstories or personalites--with the notable exception of Kreia; she is in the same league as KOTOR 1's characters. Occasionally, you'll get a juicy emotional cutscene or something where you actually connect with the others in your party, but those are infrequent. Also, the influence system makes its doubly hard to find out any stories that the NPCs actually have. (After hearing Atton make a woefully not-funny comment for the hundreth time, you'll start getting nostalgic for Jolee or HK-47 and their side-splitting remarks.)
The sidequests involve a lot of tedious running back and forth, and many quests simply cannot be completed, or end with irritating abruptness, a symptom of the game's unfinished state.
Many of the locations you visit in TSL are disappointingly flat. Unlike the unique and vibrant locales in the KOTOR 1, TSL's areas seem to be studies in how many shades of brown, gray, and black can be used (ah, for Manaan, or the Rakatan world).
There are other complaints, too: countless bugs, typos in the dialogue subtitles, items mysteriously vanishing from inventories, plot-critical quests failing to trigger, etc.--while I've been fortunate enough to avoid the bulk of these, I've heard many others complaining bitterly about them.
All in all, TSL is fun, but is lacking on many levels. If you liked the first KOTOR, I'd recommend getting TSL, but you'd be better off waiting for the price to drop.
Meanwhile, I think I feel inspired to go replay the first KOTOR, and hope that the rumored KOTOR 3 will be polish the many rough spots in KOTOR 2 . . .