I don't expect anything to be perfectly balanced, but I always want to feel like I'm playing a legitimate game without obvious issues making combat trivial. I hate that I have to ban myself from using things to make the game fun. Some relatively small changes to the game would help a lot, see below:
Glass cannon: Really now, this talent should increase damage output, not AP! Why does glass cannon turn me into a bionic man that can suddenly run or swing a sword twice as fast? It doesn't make sense and breaks combat by allowing for non-stop kiting or massive barrages of CC. Glass cannon thematically suggests higher damage at the cost of defense, not super hasted bionic limbs
Invisibility spell: No amount of int should reduce this spell to a 1 turn cooldown. This is doubly true considering no game mechanic exists to detect an invisible character. You should enforce a minimum cooldown on game-breaking abilities such as this. For example, it could have no less than a 5 turn cooldown regardless of int.
Stealth: Again, because a high stealth character is near impossible to detect, and it only costs 1 AP, using stealth in combat needs a cooldown. You could simply make it so a character can't use stealth in any round he/she has already used an offensive action. This gives the enemy a chance to fight back in between sneak attacks, and it makes sense that your character would be temporarily spotted after attacking from the shadows.
Elemental shields: I can't believe these are still doubling our HP! Come on, they already give resistances and immunities for 3 AP, that is good enough. I shouldn't be able to double my HP every turn for 3 AP, how boring and overpowered!
