So, I have focused a lot more on the Chanter than other classes as it is the class I plan on playing first. I want to get into some of their abilities and why they are probably overpowered. I am going to keep this as brief as I can.
Why are they OP:
Summons - I am unsure if summons are broken mechanically or whether they are intended to last as long as they currently do. Currently... you summon creatures during the first beetle encounter, and they can work in the frontline for the rest of the map. Three Skeletons + fighter in the front line reduces the parties need to cast spells, and increases longevity between rests far too much, IMHO. The lack of a way to dismiss Summons makes me wonder if Summons are suppose to dismiss themselves once combat ends. If this is the case then minor tweaks are needed. If it isn't the case then the summons need their Stamina Pools reduced, and/or they need only summon 1 creature at a time (3 skeletons is too much). Three skeletons also tends to clog up some of the maps... although that is another issue entirely.
Buff/Debuff - The chanter has a plethora of these abilities: They have a haste for ranged classes, they can give allies burn damage on their weapons, they can cause fear debuffs, they can reduce Concentration, they can do AoE stamina damage in multiple ways, they can Hobble targets, they can defend/reduce fear effects, etc. These are all phrases, and have no limits to uses per day/rest. They are weaved in a way that makes it like an ever changing Bard Song. They are all AoE. Used in certain ways they can really assist your party, and can be somewhat OP by themselves. I think they are mostly fine, but some tweaking to certain ones like: Come, Come Soft Winds of Death (AoE stamina damage). I love it, and have great fun with it, but I can see it being too powerful.
AoE - The Chanter has almost all AoE abilities except for the summons. So, you can buff, debuff, Damage, and CC entire groups of allies/enemies. This is a big one. I particular Culprit is The Thunder Rolled Like Waves on Black Seas. This is an invocation (spell ability that requires 3 phrase counters) that pushes enemies away from the Chanter and Stuns them (Cone spell). So, you can AoE stun enemies while pushing them away from your weaker party members. If you hit the bulk of your enemies you can really change the outcome of a fight.
My 2 cents here is that Chanters need summons tuned down (them dismissing after a encounter would be a big one), some AoE abilities (invocations) may need to be single target, and some tweaking may need to be in order for the Phrases. I may have missed something and would love more input.