so skip base and 1st expansion. Play the 2nd expansion?
NWN base-game has good story + character development, for the most part. It's worth playing for that. Just...I think the ancient race storyline is "meh". The game would be much better w/out it. The other main storyline w/ Fenthick, Aribeth and the King is much better, more fleshed-out, and more interesting.
If you're looking for BG-like strategic-style of combat+gameplay - forget it; parties are too small here in NWN base + SoU; especially for a D+D based game. You're better off w/ Hordes' campaign for that; even though Hordes' campaign still isn't on BG's level, since BG can have up to six party members. Six is a better number for a D+D campaign, anyways - as you can have more variety of classes + a more well-rounded group there in the BG titles.
Also, both NWN base-game and NWN: Shadows of Undrentide are built for starting Level 1 characters.
Another problem w/ Hordes is this: there are returning characters from base-game (Aribeth) and SoU (Deekin). To get the most out of these characters, you'll likely have to play everything.
NWN: Hordes is build for you to start with a higher level character. Likely, when starting up Hordes - you could + probably will import your character from either NWN base-game or SoU.
EDIT:
Any comment on NW2 as well? Again, I am looking for good story and good character development, like the BG series
NWN2 is really good, too. With bigger parties (up to 4 max), more orders, and more control over your characters - NWN2 is hard to go wrong with.
NWN2 is Obsidian's baby (for the most part) - so, expect the typical Obsidian staples here: epic+grand stories; interesting characters; great dialogues + writing; and excellent narratives.
If you're looking for epic traditional fantasy stuff -
NWN2 base-game has you covered. It's pretty damn good, TBH.
If you want one of the most personal stories since Planescape: Torment (it's very similar in scope there, IMHO),
NWN2: Mask of the Betrayer expansion has you covered - and is one of the best expansion packs ever made for a RPG, IMHO.
If you wanted NWN2 to ever go a bit more open-world, a bit more old-school (i.e. you can create an entire party here) + introduce a bunch of new elements -
NWN2: Storm of Zehir will fit the bill and is actually good.
NWN2: Storm of Zehir might not have the best story, characters, and whatnot - but some new gameplay elements (this feels way more open-world than any other NWN game, a new overworld map + you can also control the map w/ your caravans for making money & getting resources) make Storm definitely worthwhile. It might be the weakest of the 3 major NWN2 campaigns b/c of its emphasis is less on the typical Obsidian staples, but it's still quite good b/c of the new gameplay elements.
I've never played Mysteries of Westgate DLC (from Ossian), so I can't speak on that.