I played KOTOR II first as I couldn't find the original anywhere. KOTOR I truely is better, even after I learnt how to play etc in the second. I don't like the endings of either game actually. The Dark side ending of the original doesn't make sense with what Revan did next (Left the galaxy pretty much, or to the edges at least.)
and the second game..that just leaves you wondering what the developers were smoking at the time. Your ship falls away towards the planet core, but you apparantly manage to escape..
Apart from the endings, I thought the games were simply brilliant. Along with Zelda: Ocarina of Time, they are the best stories I've ever been a part of. The sheer volume of information, especially regarding the force etc, and all the options (You can redeem Atris, Kill her, leave her in torment..do a lot with such a minor (In terms of interaction length) character)