Im going to weigh in here. I LOVE all the infinity engine games. BG2 is my favourite game of all time. I am also a powergamer. Any sort of cheese in these games chances are I have done it in 1 or more playthroughs. for example BG2 
  
Feeblemind firkragg - Check 
Cloudkill off screen - Check 
Kensai mage solo - check 
wiz slayer thief solo - check 
multiple (3) rings of the ram - check 
spell abuse (simulcrum, wish, projected image) - Check 
Invis cheese with staff of magi - check. 
scrolls of magic immunity - check 
Using hasted totemic druid pets on mindflayers and then close the door while summons kill everything - check 
  
And here is the interesting thing - IT WAS SO MUCH FUN!. Thats right. Alot of the fun I had in the old infinity engine games was figuring out fun and cheesy ways to beat encounters. I have probably played through BG2 at least 15 -20 times and loved every minute of it. 
  
I sincerley hope that Project eternity does NOT limit powergaming (within reason) and allows players to play how they want to play!