It's not a question of plausibility, it's a question of fun and things to do in the game. In NWN single player you are playing nerfed PnP DnD alone with yourself, and a retarded DM running the proceedings. What DnD computer RPGs have always done is to add the control of several characters to make up for the lack of actual role playing and socializing that makes pen and paper DnD fun. In this sense, NWN single player is like the worst of two worlds.
Now, I imagine NWN is probably much better in multiplayer if you're playing with the right group of people, but I never actually tried, because at the time of NWN's release I was on dial up, and anyway, the right group of people wouldn't be caught dead playing NWN.
Finally, as for the stuff that has come out in the past 2 years, first you can't expect people who hated the original experience to wait around for 5 years for new mods to come out, and second, for obvious reasons, I haven't bought NWN's expansions which puts newer mods out of the picture. Even NWN2 was hard to get into due to all the NWN1 vibes it gave me.