Volo is great. He's a great stereotype of DnD Bards. Loud, boisterous... Not very good at things...
Kagha is cool. Definitely brings a different vibe to the Grove than the rest of the Druids. I really wish she'd been the companion instead of Halsin. Have her atone for her actions by aiding your party. Let her see the Shadow-Cursed Lands first hand to see why the Shadow Druids are not cool.
Lump is great. I wish he could continue with your party outside of Act 1. Would be very interesting interacting with him in the Underdark when messing with the Sussur plants, having them stifle his headband's magic temporarily.
The Bard from the cursed necklace in Grymforge. I wish he'd pop up more often to opine about things you encounter. Also, if he'd appear in camp and interact with your party. Imagine him trying to get Lae'zel to laugh!
BOOOAL is great. I wish there was more you could do with him and the Kuo-Toa. Things like as a Cleric unlocking the Domain of Blood if you choose to worship BOOOAL (BOOOAL giving more gifts throughout your journey if you keep offering him blood via the Cleric Domain or his Sickle - Such as more weapons that scale into the later stages of the game) or if you choose to kill BOOOAL and the Kuo-Toa start worshipping you instead, you get bonuses from their worship and they appear later in the game doing dumb things to "Please" you (Like more ritual sacrifices... Which you can either stop or embrace)
Alfira is cute. Also the song she sings is nice. Would be cool if she'd travel with you, writing more songs about your exploits like she mentions at the party.