D3 will have less depth than (modded) D2 does, unless I've missed something major, because stats are now auto-assigned instead of customized. A particular mod I've played recently rebalances stats by making STR, DEX, and NRG critically important to your ability to do damage with weapons or spells, in addition to existing effects. You can still get only your minimum stat requirements for weapons and dump the rest into VIT, but your damage will be so pitiful you'll be unable to kill anything in Hell or even late Nightmare; but at the same time, funneling everything into your DPS stat will result in a glass cannon, making survival difficult unless you're extremely careful.
You're free to customize your character how you want - DPS in exchange for survivability, HP in exchange for DPS, or something in between. You can beat Hell difficulty and beyond with pretty much any combination, though some might perform better than others.
If Blizzard felt the stat assignment system was unbalanced, the solution was to fix it, not fucking remove it. It's like taking the radiator out of your car because the fan was broken.
"Stat customization," as you describe doesn't really apply; the previous games had that
in addition to being able to customize your stat allocations with each level. Do you understand?