Dantooine in K2 wasnt too bad, but I still prefered it in KotOR1 and it seemed much more explorable. Nar Shadaa for me was pretty good, lots of sidequests and plenty of places to explore so it certainly entertained me and kept me interested when I was playing it the first time around, probabally more enjoyment the second time around because I knew what was happening and what to and what not to do.
Onderon was alright, Dxun was quite fun but I'm sure there could have been more things to do on it, more exploring like the Kashyyyk shadowlands and more quests were needed for it I think, yes you did get a handful but only about half required you to go deep into the forest. Onderon was the same, you really had one thing focusing on, getting to the Queen or Palace and only a few major quests came up not many small ones like in Nar Shadaa, and I would have liked to explore more of Onderon.
The Citadel Station was too short IMO.
Korriban just sucked.
And likewise with Peragus.