Did you ever talk to your companions?
The influence system was a poor substitute for C&C. All it did was force you to kiss your party members' asses to unlock content necessary to fully understand the story. It actually undermined roleplaying by making you behave contrary to how you'd normally want to, and provided no alternative reward. Plus it was pretty broken, especially in Mandalore's case.
It wasn't substitute. Reason for its existence was to replace the Bioware's standard, moronic "oh you gained new level. You know I have no reason to trust you at all but let me tell you my deepest traumas and darkest secrets so you can unlock my special mission later in game".
And it was broken only on Mandalore's case - and that's due to the cut content
That is just silly criticism. It isn't criticism at all. You ROLEPLAY your character. If you get out of character to kiss some character's ass then you're simply metagaming/whatever to get "all teh goodies". Then again if you're roleplaying manipulative character fawning and stroking your companion's egos etc. would be way to go. Or just roleplay different character that agrees with different party members on your next playthrough.
Maybe your LS paladin of mighty justice with lightsaber doesn't do well with HK-47. Well, you can try to infuriate him to point he just doesn't care about telling his secrets out (like random_n00b said. It works with everyone) or maybe you just shrug it off and gain points and benefits with another party member.
Next time play badass sith who just loves HK-47. Cue to all the bonuses and stuff from him, but character like Disciple or Handmaiden would propably hate you. No "goodies" from them then, boohoo
If your (natural) INT score is good enough you can also intuivitely guess stuff about Kreia for example.
Way you could reflect and define Exile in superbly written dialogues is on entirely different level compared to any Bioware game, namely K1.
What was the last great game Sega published?
Sega has numerous awesome titles under its belt currently (and I used to be one dissing Sega). For example the much beloved Total War series
How's that different from other quests? There was a merchant on Yavin station.
Slave deal isn't that big. But if you make deal with slavers you can come and get your share of profit every once in a while. There was some cut content related to it too.
The merchants... other one has a lot better inventory, other one has weak and not as good rewards. However if you choose to aid the weak one later in game after stabilizig Onderon and other planets you get some of the best stuff in the whole game from the merchant who has now made trade deals with people on those planets.
In K1 you could kill Juhani, side with either gang on Taris, side with one or neither of the Sith masters on Korriban, kill most of your companions. None of this stuff is world changing, just the usual RPG quests with localized consequences. Actually K1 did have something world changing, you could poison the shark on Manaan and make health packs rare and expensive. But this small stuff is not really C&C, let alone living, breathing world you're influencing.
There's only one decision in Kotor 1 that really, really matters. Killing your companions and such are directly tied to it. Well, minus Juhani. That's some good C&C you're right about that. Sith deal on Korriban too somewhat. Then again in K2 you can get 4 different party members depending on your gender and aligment. And cause death of Visas on Telos. There was a lot choices around Nihilus fight. Too bad cut content and way too easy Kotor combat system ruined that. Well, TSLRP should take care of that...
Poisoning the shark didn't make medpacks rare, it only made them more pricey (100 creds or so IIRC). Of course in the end of the game you were drowning in the cash so it didn't matter.
And those are small scale C&C. KotOR 2 would've had some additional really major ones - namely the whole ending sequence in which all your deeds mattered. HK Factory stuff defines (which you couldn't know forehand) fate of Malachor V, your standing with the companions define what kind of conflicts happen... You could also choose to abandon your companions and not resuce single one of them. In battle of Telos (in early drafts) you could also end up joining Nihilus and/or go blow up Republic's command ship, Sojourn (bye bye Carth!)
Oh, and you also would've been able to destroy Citadel Station.
Then again Kotors aren't paragons of roleplaying. However Black Isle's Fallouts and Planescape Torment ARE. And Obsidian Entertainment's design philosophies and core people have worked on those very titles. Heck, MCA was lead designer of Torment and all by himself wrote HALF of the humongous amounts of written text in the game. OE also has people of Troika's people on board (and both Bloodlines and Arcanum contained a lot of roleplaying and C&C. Esp. Arcanum which might be only title capable of challenging Fallout when it comes to C&C), namely Brian Mitsoda.
Really, I just don't see where your disbelief come from. There's no basis for it, remembering the people and design philosophies involved here