The only world I played when I played (online) NwN was
Argyle Online
However - it is a very hard world to play because of a select few things:
It is hardcore roleplaying. So limited out of character convesation and meta-knowlegde is to be used.
It is perma-death. Sure you can be resurected, but that is not likely - unless you are close friend with a higher level priest.
It is full-PvP. Although when I played it was a very mature crowd, so PvP was limited.
It is very low magic. Finding MW weapons is hard. Finding magical items is very hard.
Mage-Hate. The lore of Argyle speaks of a distrust of magic and thus wizards/sorcerers. Tension is around.
Race-tension. Races dislike and distrust each other (on various scope).
Monsters are hard. They have improved AI compared to the single player games by far. This means you can easily die to the lowest monster around - combat is hard and dangerous.
XP rewards match pure PnP much more then NwN-rules. So don't expect to level fast if you survive combat.
Further more it uses Amour movement changes (can't run around in heavy armour as fast as in light), D&D 3.5 rules instead of 3.0 and most are modified to match the Player Hand Book (which means no cheesy summon spell durations) and much much much more.
Also - it isnt' Forgotten Realms - but a whole new realm with its own lore and history.
AO isn't for everyone - but if you are a roleplayer then it is certainly worth a look.