It doesn’t matter how many if there’s virtually no strategy involved. The orbs are always there because you’re always killing things. There’s no decision to make because windshielding monsters keeps you healed almost all the time. On top of that (and the big collection of potions you’ll accrue), equipment can regenerate your health, the first follower you get can also heal you, and you also get unlimited use of town-portal fairly soon.
The most limiting factor in the game is that you have to wait while your character walks from place to place. Walking feels almost like a silly waste of time, because otherwise you hold the mouse button down and turn streams of monsters into meatgrinder paste and loot. All the walking does is slow down the pace of slot-machine lever pulling.
If enemies formed living walls to block your path instead of attacking, the effect would be almost the same.
Emergencies would make it more interesting to play, but they are pretty much completely absent on normal difficulty. For all the crunchy violence, it really is just too casual to maintain any tension.
I wasn’t going to say this, but they’re right, D3 does almost play itself. There might be a good game there, hidden in the higher levels or harder difficulties, or behind too many hours of boringly easy-street intro play, but the beta sure hasn’t revealed it.