The expansions were actually pretty nice, the multiplayer was far stronger (I don't know how NWN2's multiplayer is now, but at release it was a mess) and the modding tools were easier to use, so we have a LOT MORE mods to play with, though, to be pretty honest, the average level of quality is lower than NWN2's.
Also, some found the interface and absence of a party better, not to mention that the combat felt more alive with NWN's animations (.... they screwed up attacks of opportunity though, so I'm glad that Obsidian took them out, though they could have done a better job at making combat interesting to see).
If the add ons were goood I don't want to slander them. But the original campaign was as much fun as being ordered around by that wheelchair guy in Little Britain.