IMO, the expansion packs are actually better than the original game.
The NWN OC is a travesty: the AI of henchmen and hostiles has all the IQ of a dense, dense ball of mud. The story is ridiculously predictable. The NPCs are about as memorable as a generic X'Mas card. Aribeth's voiceacting is flat-out squeaky. Each chapter is a repeat of the last: find four pieces of artifact, hand them to someone, and fight the chapter's big boss. Blocky graphics that are a year or two outdated at the time of release; tilesets that make everything look the same; crate-smashing. Boooring.
The SoU OC is somewhat better, but still continues the trend of "find four pieces of artifact" with some roleplaying options thrown in. I didn't finish this, however. It didn't keep my interest long enough. Deekin is way overrated as a comic relief gimmick.
The HotU OC is the only one worth anything, but it's still underwhelming (especially since I played it after KotOR). The storyline's intriguing enough, the quests, puzzles and such good enough to keep me playing (two times, actually), and it redeems NWN as a whole somewhat. Better graphics, better AI, better henchpeople. Shame it's a bit short. The last chapter is a bit of a mess, though, and is basically a series of puzzles after another. Yeeek.
If you buy it, buy it for some player-made modules -- and skip the OC in the original and SoU. Many, many fan-made modules are light-years superior to the first two official campaigns.
