I`ve just beaten the game on hard mode and i`d like to share my thoughts. Maybe somebody will find them useful.
1. What race to choose? Choose race with best options for your play - infravision or fast movement, for example, don`t look on stats because difference in 3-5 points doesn`t matter.
2. What class to choose?
In my opinion the best class is inquisitor, because he has the best abilities. His first ability is immolate. It has fire damage and lasts for 3 turns, and it`s range ability, and when you cast it turn after turn you double the damage, so it is much better than slice for example (which can only be used with specific type of weapons) or useless abilities for +3 damage or +5 strenght.
He also has most abilities with stun (and fear effect) - which is the most useful abilities in the game: Intimidate (fear for 3 turns), shield throw (range stun for 2 turns), seven deadle sins (the best ability ever stun and bleed,poison, etc effects for 3 turns, and silence heretic (enemy can`t use any abilities for 5 turns). If you lucky enough you can also find stun abilities of other classes (for example flash bomb). So using these abilities you can stun any enemy for more than 10 turns (and repeat). Inquisitor also has cleanse ability, which cancel any bad effects such is fear, poison. etc - very useful sometimes.

I can also name the worst class - it`s fallen knight. Most of his abilities are physical attacks with range 1. So it`s better to attack with 2 weapons than use most of his abilities. After beating the game with inquisitor, I tried fallen knight and was killed by 2 enemies: tiger and lion. When I was inquisitor they didn`t even touch me. And there is also such ability as revenge which can kill any melee player. I don`t know how to kill last gods-bosses with melee fighter. You also have to repair clothes and heal damaged health - because every fight you will receive damage.

While leveling up you will also choose abilities of other classes, so there is no pure class. Every play is mix of many classes. So here my tips for choosing abilities:
1.Take abilities with stun/fear/silence - it`s much better not to take damage at all and hit the enemy lightly than hit enemy hard with receiving damage. It is hard to regain health during fight (there is some abilities - vampiric touch, etc but enemy can hit much harder than the amount of health you regain during the turn.)
2.After that take abilities with biggest range - lighting, explosion, acid split, death ray etc. (enemy won`t even touch you, while you attack him) - some enemy`s abilities is very very painful but has the range 3-4 tiles. So if you hit him from 8-10 tiles he won`t get you.
3. Try to have at least 1 ability to run away (roll back, vanish, fast step, etc) until you find artefacts with phaseshift or teleportaion (the best escape and travel ability (wings) - with 90 stamina teleports you to any spot on the map - you must always use it - to repair things and rest (until you kill god that cancel durability or artefact with repair).
4. It is good to have some summon abilities (you can also gain near 3-4 abilities to summon different allies by killing gods (summon vampire, dwarf throw, summon deer, summon tree, etc.)
5. Any range ability is better than melee.

For example let`s compare first abilites of inquisitor and fallen knight.
Inquisitor casts immolate when enemy is 3 tiles far from him, so he makes 3-4 attack before enemy even touch him. When enemy is near him - he uses intimidate and disables enemy for 2 or 3 turns causing enemy to fleet away 1-2 tiles. All this time enemy is damages by immolate and don`t attack the player. You can also walk away and continue damaging enemy. So you attack for 5-10 times before the fight even begin.
Fallen knight start to receive damage from the first round of fight or even before it if the enemy has range attack. So the choice is obvious. It`s also very funny that fallen knight has one of the best ability for range player - shield slam - when enemy is close to you you can sent him 5 tiles away and continue to use range abilities. The problem is the most abilities of fallen knight is with range 1. So if you play as range class (warlock, poacher or inquisitor) always take this ability.

3.What stats to maximaze.
Every level you can choose what stats to grow:
1) Intellect - it scales damage from any elemental weapons (no matter of type) - it`s the main stat in the game, because best weapons are elemental. Choose only weapons with pure elemental effects (without physical, otherwise damage will count 1\2 from intellect and 1\2 from str\dex. Intellect also maximaze the chance of making best items with biggest elemental damage.
2) endurance - every level you should spent some points in endurance beacuse it`s your health and physical resistance.
3) willpower - it`s your magical resistance.

Strenght and dex are useless if you play for any range class with elemental damage. During the game you will find enough items to boost your strenght to carry much weight and dex - to boost hit chance with elemental bows and crossbows.

It doesnt` matter what ability you use with physical of elemental damage. Damage will count from main weapon type ( strenght - axes,swords, maces etc; dex - spears, daggers, bows; int - any weapon with elemental damage) and damage type of the weapon.

4. Before fighting emperor and last bosses try to kill all other gods - they will give you useful abilities after killing. Find their weak places - they can have different resistance and some weapons and abilities will be useless.

5. If you don`t have shield slam and shield throw and other shield abilities (reflection etc.) I`l advice you to use elemental bows\crossbows (damage scales of intellect) - some range weapons have attack range of 10-12 tiles. Or use weapons with best damage (scaling with your int\str\dex) - to maximaze damage of your abilities.

6. When fighting bosses try to summon different allies - to make boss atack them not you or you won`t last long. When summon allies always use ability command allies - or they won`t attack anybody for some rounds.

7. Always try to have some water with you (you can craft goat skin from leather - killing cow or deer to have enough leather or salvage sandals).

8. Crafting is almost useless until you kill the god of smithing - after that all crafted items has no durability. Until that you can receive anything from looting.

9.When you see glowing wall (it has a bit different colour than other walls) in dungeons it means there is secret path. You also can go throught waterfalls, there will be secret path too.

So that`s all. If I remember something I will add it to this manual. Thanks for reading.