Right, it's definitely worth checking out other premium modules, too, instead of limiting yourself to the Kingmaker set.
Pirates of the Sword Coast is very enjoyable, though there is an episode where you are marooned on an island. That's the part I really hated, but I didn't regret playing through it - the rest of the module is very good and includes some innovations such as underwater areas and others I can't mention if I want to avoid spoilers.
Wyvern Crown of Cormyr has got probably the best atmosphere out of all NWN modules I've played, strengthened by its soundtrack. The story is enjoyable, but not fantastic. It is the only official NWN module or campaign featuring horses, which some hate, but I find them cool. You don't really need them for the most part, too.
Infinite Dungeons is hack'n'slash and almost no role-playing whatsoever, but these few dialogues and item descriptions you'll find are humorous and quite interesting. Its main premise, though, is stated in its name - you can explore randomly generated dungeons. If you're into that kind of gameplay, it's very neat. The good things about Infinite Dungeons is being multiplayer-compatible and suitable for characters of any level. It's a perfect final destination for characters you finish other modules or campaigns with, but want to keep playing with said characters. The huge downside is that the loot found is incredibly overpowered, but I've created a mod that tackles this issue, if you'd be interested.
Darkness over Daggerford was meant to be a premium module, but was released for free as an unofficial one. Still, its quality matches, if not surpasses, the best official premium modules. It has got a very baldur-ish feel (and even makes some references to Baldur's Gate a few times), so it's definitely a treat for any BG fan. I've also found a reference to Pirates of the Sword Coast, not sure about any other modules or campaigns, though.
Story-wise, you don't need to have played anything before these modules, but here's what I've noted while playing them:
-Pirates of the Sword Coast takes place soon after the events of the original campaign
-Darkness over Daggerford takes place some time after Pirates of the Sword Coast
-Infinite Dungeons takes place after Hordes of the Underdark - as little story as there is to ID, the events from HotU influence Infinite Dungeons quite significantly