NWN: Blocky, blocky, blocky tilesets. Every city will look the same; every dungeon will look the same; every cave/mine will look the same; every inn will look the same. Not exactly eyecandy. Its D&D (not AD&D) 3E rule implementation is questionable, and flawed in places, but this shouldn't be a problem unless you're a hardcore PnP D&D player. The NWN official campaign is atrocious in its story, writing, NPC AI, and repetitive nature of gather-four-pieces-of-artifact chapters. Bit reminescent of D2, but with much better attention to detail and more original quests. The SoU official campaign is rather dull. HotU is another story, though. Its official campaign is actually quite good -- many light-years ahead of the NWN and SoU OCs -- and certain improvements/additional contents make a big difference. (Robes, skyboxes, epic levels, bigger party, etc.)
D2: Well, if that's your cup of tea, sure, why not? As an action game with RPG elements, it does what it's supposed to do.
IWD: The first one (plus HoW and Trials of the Luremaster) is at least worthwhile, I think -- if you're looking for a fun dungeon crawl. It's no clickfest like D2 (a bonus for me, of course); it requires more tactics and micromanagement. It, naturally, has much better RPG elements all around. Superior graphics, story, writing, dialogue, and atmosphere as far as I'm concerned (and lovely music). IWD2 is not half as good, unless you like puzzles and hordes of enemies that overwhelm you by sheer number, and a badly balanced loot distribution.
