Playing an offence-minded caster, it's been a frustration while doing low level solo quests to realise that most of the bosses seem to have elemental immunity or SR. While this might not be an issue to melee-capable PCs or summoners, it does really mess up low level mage characters if they can't find a team for the basic quests everyone else solos. I won't go into details, but something like 4-5 of the low level quest bosses have some form of total elemental immunity or Spell Resistance. It's not a total bust, summons are easy to get hold of at least. It's more of a style thing to allow PCs based around blowing stuff up to blow up some weak bad guys.