Whoever said that the developers captured the essence of being a LS Jedi much better is exactly right. Most of the DS acts are extreme and unnatural and require you to detach yourself from your character in order to play. In otherwords, it's pretty much impossible to truly role-play a DSer because the acts you have to do are so cruel and inhumane that few people actually would willingly make those decisions. What I think is missed in KOTOR1 that is done better in TSL is that there are many ways to be evil, and few of them require you to shake down some unlucky guy on the street for some extra credits and then kill them. Arrogance and threats, pushing people around not for the credits but to demonstrate your power over them, back-stabbing and engineering plots to cause havoc and desolation are more believable and natural acts for a powerful evil person. I mean, how stupid did you think it was when Darth Bandon shows up and force pushes some noname soldier into the equipment causing an explosion and killing him? You wouldn't see Darths Malak, Maul, Tyranus, Vader, Sidious, etc. doing that just for kicks. When you're evil and powerful, people that low on the totem pole are beneath your worth or notice unless they personally mess up.
The biggest unfortunate affect of playing DS is that you tend to favor the "Maybe I'll just kill you instead" option and miss a lot of the story, character development, and history. You should definitely play LS first, and then DS for a change of pace, to see what other options you have, and for amusement. Because if you can detach yourself from your DS character, the DS acts and responses from your party members and the other characters you mess with are quite humerous. For example: after you kill Jolee, Juhani, Mission, and Zaalbar and board the Ebon Hawk for the Star Forge, "Darth" Bastila receives the transmission from Admiral Dodonna and Master Vandar and Dodonna relates how they are being slaughtered by the Sith. Bastila turns to your character with an amused look and your character gives an evil smile and shake of the head that is pure hilarity.
Also DSers have the more powerful Force powers. I find that most of the LS powers are a waste for my style of play because their affects just don't last long enough to make them useful in pitched battles...the Aura and Valor lines in particular. Only the Heal powers really trump any DS powers substantially IMO. Insanity=Stasis Field, Force Storm=(almost)Destroy Droid (actually Force Storm seems to work better for me vs. droids). And the DS mastery bonuses of +1d8 damage for Guardian and Immunity:Poison for Sentinels are IMO better than the +3 STR (given that most people will use their DEX bonus for their Attack Roll) and +3 Con repectively for LS (LS Consular bonus is much better though). LS makes up for these deficits however by having the better items. Circlet of Saresh and the Star Forge Robes plus the Solari crystal are generally far better than the DS options.