KiNgBrAdLeY7: My definition of game break in this one...
1) Be a two faced, greedy bastard (for example, help both goblins, and trolls, and then eliminate all goblin city in righteous self-defense). After that, march into troll territory, kill them all, no one cares.
2) Rob the bank. Side quest and very ludicrous in both loot and xp.
3) Let your would to be victim, such as Garry the bank owner, see you enter their private areas; they attack, you can kill on self-defense, guards won't trouble you later if done correctly, even his own, damn fiancee, does not notice him being dead... And he even reappears in the working-npc-time-patterns in his bank, in his place, but simply dead (corpse); bank, guards and co operate as normally!
4) Summon the woman Ylside once to kill her to get her armor and sword (this sword is good against Akbaa or serious enemies such as the lich). And like 10 to 20 more times to kill her afterwards (after hitting level 9) to get max xp and hit level 10 (you cannot max your character with only quests).
5) Just before assaulting the final fortress with the temple of Akbaa, after finishing all quests and cutscenes, cruise through ALL levels, and slaughter magnificently EVERYONE, and EVERYTHING! To the last man/woman/child/chicken/pig/lover/king. There are no consequences, you still saved the world, Yay! Yet, in an additional, different definition/interpretation/meaning, but oh, well...