You should read some guides first, like Sombrero's: http://steamcommunity.com/sharedfiles/filedetails/?id=1133139481

Don't worry too much about "classes" nerfed or not. Nearly anything is viable.

Most important to know is that there are two forms of armor, physical and magical, and health is usually only reduced and CC applied after the armor is gone. Most mobs have one armor (much) higher than the other. It makes not much sense to remove both armors on one enemy.

So a classical group, tank (real tanking is really difficult in this game), physical ranged, magical ranged, healer is not the very best composition of a party (but possible). You can focus on one damage to remove one of the armors fast (for example: warrior with one-handed and shield, two-handed warrior (combined with Necromancy for example, a magical school with mainly physical damage), ranger (or rogue) and summoner or split the damage in your group (two physical, two magical damage) and attack two enemies a time, according to their lesser armor.

Choose wisely the difficulty level, you cannot switch back from Tactician, the highest difficulty, to lower ones. Tactician is really difficult, you need a bit (lot) of min/max, item hunt and reloading to master. I find it more a burden than a delight. I prefer Classic, but some might find it boringly easy.