I've never liked cooldown systems, or at least I've never enjoyed playing a spellcaster in a game with a cooldown system. If Obsidian somehow think they can do it better than all the other games that have tried cooldown systems, then go ahead I guess.
Personally I'm kinda at a loss though. The IE engine games didn't have particularly great combat, but if they did one thing right it was the spellcasting system. The spells and spell selection/variety/power was great( particularly in BG2), the spell battles were probably the best throughout the history of gaming, and spellcasters were without a doubt the most fun classes to play.
So why change the single-most successful thing the spiritual predecessors to this game had?