It's not the age of the game that deters me. In fact, I think one of the reasons I dislike it is because I keep comparing it to the IE games, and it feels a lot more restricted.
As for what everyone else said: I did hear bad things about it, too, but I figured that it was probably just "not good" instead of "bad".
Is there anything like BGTuTu for NWN? I heard you can control companions in NWN2, like in Baldur's Gate, which was my biggest problem with the game. I may decide to reroll as a melee-oriented class, though. Are the expansions to NWN closely related to the main campaign, or only tangentially? I hear that they're better (particularly HoTU). I do have the diamond edition, so maybe it would be worthwhile to do those.
You can use your NWN character if you want, but Shadows of Undrentide is a completely separate game. You start off as a beginning adventurer, training at a school run by a dwarf mage.
Hordes is, again, completely separate from NWN and allows you to build an epic level character. Your character is "carried over" so to speak, from Shadows. Eventually you will run into a few familiar faces from NWN, and can have Aribeth as a henchman, as well as Deekin. [the Doom song has been around for a while]. I did enjoy Hordes more than NWN. Some epic builds: http://nwn.bioware.com/underdark/character_builds.html
NWN2 is not the same, and wasn't made by Bioware. You can control your party; unfortunately there is a "forced party" type of thing going on that I really didn't like. I really hated the ending. Masque of the Betrayer was better, imo, although there were minor story/party issues with that one for me as well.