In BG1&2 you pretty much always ran at least 1 cleric, 1 mage, 1 thief, 1 tank. That makes the games play very samey. You have a thief to pick locks and traps 100% of the time. You have cleric to give you the same basic buffs 100% of the time. You have mage to haste you near 100% of the time. You have 1 frontline guy aggroing the enemies 100% of the time. You don't make any real compromises and have no weaknesses.
So far I didn't like RPGs with only 4 companions. That said if the map and quest design is good enough... What if paths will be varied enough to not require "trap and picklock" guy? What if we won't HAVE to have priest for buffs and 100% protection from things that are bound to kill us otherwise? If those things that you usually HAVE to have will become optional boons opening new paths... that could be interesting.