BG: you can cast spells whenever you want.
PoE: no, only in combat!
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BG: you can make a bad character, if you want.
PoE: no, whatever you do, your character should be decent.
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BG: you can get broken, crazy, items. Cloaks that turn you into wolves, rings that double the amount of spells you cast, wands that paralyze even some of the most powerful enemies etc. (and I'm just naming BG1 stuff here).
PoE: no, it's too much! Have a sword that does a bit more damage or an armor that's a little bit more protective.
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BG: you can run straight to powerful monsters and kill them for tons of xp, if you want.
PoE: no, you play the game our way. Killing monsters doesn't yield xp, you're supposed to do quests, even if it's your 500th time through the game and you've seen every possible outcome.
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BG: you can multiclass and dual-class.
PoE (1, at least they fixed that in 2, holy hell): no, single classes only!
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BG: mages can buff, summon, do damage, polymorph, debuff etc..
PoE: no, that's too much power (read: fun) for one class. Divide them up into several very narrow classes.
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BG: you can move around as much as you want during combat.
PoE: no, sit still while you're engaged.
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BG: here's a level 1 spell that can instakill an enemy and here's a spell that can turn even the final boss into a squirrel. Have fun.
PoE: no, almost all mage spells should be 'do x amount of y type of damage', that's more balanced.
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BG: your druid can stay shapeshifted for as long as you want. Hell, pretend you're a bear permanently if you want.
PoE: no, shapeshifting only in combat and only for a small amount of time!