Like many CRPGs, some race, class, and skill choices are better than others. Read this brief guide to understand how to build a strong party that will serve you well throughout the game.

After much experimentation, I settled on the following party to beat BT4 easily

Front Row:
Dwarf Fighter, Dwarf Fighter, Dwarf Fighter
Ok, it's a bit boring I will admit, but there's two things you want your front line to do.
1. Absorb damage
2. Protect the back line
I choose only the Dwarf race for my front line fighters, because Dwarves are the only race that cannot be pushed or moved, and if your front line gets pushed or moved then your enemies can attack the back line with melee attacks.
It's important that your fighters are not moved. Not because they have lots of hit points or lots of armor, but because they are the only thing standing between your squishy back line and death. Further they have the best front line skills in the game, and it's not even close.

Defense
Heavy Armor and CON of course
Critical Shield Block - this happens much more often than the 10% would indicate
Quick Reflexes - once you get this you will block nearly 100% of incoming attacks and take 0 damage
Shield Bash - Can stun melee attackers when you block them, and you will block about 100% of the time

Attack:
Vanguard - all your Fighters should have Vanguard so they can use 2H Swords and shields.
Sweeping Slash - Great to hit 3 melee foes at time, makes your front line fighter good damage dealers, although with Champion, you can really just stand there and watch melee opponents die
Sundering Smash - Good to remove enemy armor and many of the late, higher level enemies have lots of armor, so you will need this and Biting Taunt to strip it
Get all the Sword Crit abilities for extra damage

Command:
Commander (only for 1 of your fighters, and it should be the one that off to the side)
Champion - maybe the best (other than Shield Block) fighter skill in the game. Once you have this Shield Block, and Vanguard it easy mode for melee opponents. Once you get this you'll love enemy melee opponents who strike you multiple times. Your shield will block all of their attacks and your Champion counter attack will hit them back for each time they attacked you for about 30 points of damage each. Once I had this skill and Vanguard and Shield Block I could just let my front line stand there and all the melee opponents would die.
Taunt and Biting Taunt - make them attack you, strip their armor, and then retaliate with Champion

Back Line:
Why 3 Outlander Humans? Easy, the back line will get hit most often with Bleed, Poison, and Fire attacks and if you're immune to those your back line will take MUCH less damage. While it's tempting to take Baed Humans for the extra skill points, resist the temptation as the Outlander Humans will make your back line much tougher and you'll be very happy with the choice, especially late in the game when the opponents will hit your back line with Bleed, Poison, and Fire often.

Outlander Human Bard - come on it's Bard's Tale for goodness sake! Honestly, Bard's aren't really that strong and you could replace with another Rogue or Practicioner if you wanted to, but I liked have a Bard in the party for variety and I loved the Bard character creation screen when he/she jams the electric guitar. Be sure to get the Grand Rabble Rouser skill.
Outlander Human Rogue - I went with a Sniper, Assassin Rogue with the Bow/Dagger Crit Skills, and Strength plus the Subterfuge skills. I found the ranged multi target damage of the ranged Rogue was way better and more versatile than melee even through melee does do better single target damage. However, since my Rogue is in the back row (because like all non-Fighters they are very squishy) ranged attacks work much better and let you strike any opponent.
Outlander Human Practicioner - Focus on skills that do mental damage as your Practicioner's main job will be to disrupt the focus of the opponents. Focus on Arcane Barrage, Mangar's Mind Jab, Meditation (get the +1 and 2x Meditation options) to build up SPs fast. You'll want maximum Intelligence to maximize your mental attack damage. Other than that choose whatever you want as your 4th skill.

With this team your front line is immovable, unhittable, and does great damage against melee opponents due to 2 of 3 Fighters doing high damage counter attacks due to the Champion skill and able to draw attacks and strip enemy armor as needed. The back row is all about damage amd utility and the Outlander Human racial choice will ensure that they can ignore some of the high level enemies worst attacks late in the game.

I really enjoyed playing BT4, and with this winning party, I hope you will too.