I'm okay with the current bunch. I like Lae'zel and Shadowheart for the most part, indifferent about Gale and Wyll (never recruited Wyll, tried recently but since I'd already done the goblin fort...) and have a slight dislike for Astarion. One thing I keep experiencing in RPGs though is that characters can very quickly become a lot more interesting when your initial feeling was indifference or resentment.
More companions would certainly be nice, though I have no strong feelings about what they should or shouldn't be.
EDIT: I only found out about Karlach in the last newsletter (hadn't really explored that area previously), so I quickly backtracked to check out that content before it changes on launch. Think I'll like her though her whole heart situation is a bit unique snowflake for my taste. Time will tell I guess.