Karlach, Halsin, Jaheira, and Minsc should never have been companions IMO. There just wasn't enough time to flesh them out before launch (they were all initially intended to be just quest NPCs). I applaud Larian for trying, but I feel it was a bit too ambitious.
Let's hope they continue to work on them (and Wyll) for the Definitive Edition.
Fingers crossed they keep working on them. Karlach at least feels more fleshed out in the beginning Acts and can join the party straight away. Wyll too from what I know(but I haven't used him as much so I could be totally off the mark).
Larian Studios your game is soooo good, please flesh out these characters!!!
