And of course all I can attempt to do is assure you that there's going to be plenty of build potential, plenty of customization, and plenty of math to dive into, if that's your thing.
Fine, and wouldn't manual stat allocation provide even more build potential, customization and maths? :P
Anyway, I find the stat allocation freedom something very caracteristic from Diablo. If it's going to be missing in D3, it really dissapoints me, and I consider it a bad start, in all honesty. I myself don't want to see a new game, I want to see a sequel to the series, another true Diablo, in fact, a continuation to the storyline with the very same mechanics present in LoD with new graphics as shown of D3 to date, will be enough for me.
If I were asked to divide the Diablo's aspects in percentages based on their importance, our characters will go for a 40%, lore for another 40% and items, drop mechanics and art in general will be the last 20%. Something as critical as character stats shouldn't be put into generalizations, I of course don't know how the current system for stat allocation works, but the most common way of thinking about it would be Wizards' stats predominantly going into Energy (as for D2), since they are suposed to use mental powers and magics. What happens if I decide to roll out a melee Wizard? Are those stats going predominantly into Strength? Does auto stat allocation reduce the posibilities of the way I can play a certain class? Yes, I do think so.
Implement manual stat allocation and add an 'Automatic' button in the character sheet for those who want to set their stats automatically upon level up.