Ok, I could give you a quick overview on some of the NPC mods:
Solaufein is a chaotic good (or chaotic neutral, it depends upon your alignment) Drow Fighter/Mage who can join you party after the Underdark. He is romanceable by both genders
, has lots of dialogue (with other party members, too), but adds some difficult battles for those used to the "standard BG2 difficulty level" and can be considered a bit overpowered. He is one of the older NPc mods and as such mostly bug-free.
Valen is a chaotic evil vampire fighter/thief who can join your party once you have enough gold to pay Bodhi
I haven't played with her very much, so I don't know a lot about her dialogues, but as she's a vampire, you should stay away from the sunlight and clerics turning undead. Also remember she is
really evil (must have to do with the lack of a soul
) and will force you into some battles. She is really overpowered at higher levels. There is no ToB content for Valen.
Tashia is a female elven sorceress found in Trademeet's Inn. She is romanceable by male elves, half-elves and humans, has a lot of dialogues and some added quests, too. She is somewhat more difficult to romance than the "Bioware romances" and is considered a bit overpowered, too (mostly because her "pet", a summonable panther immune to time stop, among other things)
Kelsey is a male human sorceror found in the government district. He will romance female characters and has a good deal of dialogue with NPCs, too.
I'd consider him the least overpowered of the four until now (as non-overpowered a sorceror can be
).
Chloe is a female human Kensai who can join you party in Irenicus dungeon. She's like you the decendant of a god and a mortal, her mother is the godess Akadia. She will either romance female humans, half-elves and elves or Imoen, and has a lot of banter with other NPCs, too. She joins with her own special swords that are pretty powerful and get upgraded once during the game. There's no ToB content for Chloe as of know, and there are some minor bugs in the latest version (but nothing critical).
That are all NPCs Mods I can tell you something about, hope that helps