Lack of flexibility is the downside of forcing a player, and probably the companions, into designated roles. If you jump around the skill trees rather than advancing along one tree you/they wont be powerful enough to defeat the stronger enemies. Goodbye jack of all trades, master of none characters they wont be able to cut it and I think that's a real shame because play style should be the player's choice not dictated by the developer because someone decided Mass Effect's combat system was just absolute best.
8 slots probably is going to be enough for rogues and warriors 80% of the time, they've never had many active abilities, I'm more concerned about mages. I'm horrified by the idea that despite having 4 skill trees and a specialisation that 8 is all I get per fight.
Situational spells that sit on the quickbar patiently waiting for their moment aren't going to be used because I find the idea of reorganising the bar to match an encounter to be as tedious as the whole no healing thing, especially if I have to do it for the entire party.
I'll be buying the game because I think the story is going to be interesting but everything I hear about the combat makes me wish killallhostiles was still going to be an option and hope that the modders quickly find a way to negate most of it.