It depends on how you play the game. I think side quests can take the fun out of the game at least the first time round as they are not involved in the plot. Plus as I like things more challanging the first time I went up against Irenicus with a L11 party. Needless to say my party got wiped out pretty fast leaving me with my weak little elven sorceror who had run out of spells. So I had only one option SLAYER
Plus leaving side quests means it is great for replayability the next few times you play
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"I was born of darkness. My fathers eyes closed before mine opened. I am not of this world or the other, and I have the right to be what I am..."