Perhaps its too early to tell, but from what I've played I was not impressed.
Discipline seems unnecessary to me. Hatred is on its way to becoming half Spirit, half Arcane Power, which makes it unique sort of, but not really.
Each active ability we have access to under level 14 is overall underwhelming to me thus far.
I would like to see runes show up in the beta for level 13 characters.
Most likely I'll start with the Monk or Wizard first. The destructive force they posses seems much greater than the other classes to me.
Discipline is perfectly necessary. Other than Preparation, which generates Discipline, none of the Demon Hunter's utility/defensive abilities have cooldowns. What this suggests is that Discipline acts as a universal cooldown for all abilties, that can be stored for burst usage.
It's true that Hatred isn't completely unique, but I don't see why it needs to be. You say it is half Spirit, half Arcane Power, but I think if you really look at the resource systems, you'll see a pattern.
Fury ------------------ Generated via specific skills. Decays over time. Small pool.
Spirit ----------------- Generated via specific skills. Does not decay. Small pool.
Hatred --------------- Generated via specific skills. Slowly regenerates. Small pool.
Arcane Power ---- May be generated via skills. Rapidly regenerates. Small pool.
Mana ---------------- May be generated via skills. Slowly regenerates. Large pool.
Notice how the first four (new) resources are each a step away from the need to constantly use generators and stay in combat. Effectively, all of them are derived from the opposite philosophy of Mana, which we can call Energy. Instead of a large pool acting as a long term limiter, you have a small pool acting as a short term limiter.
Beyond that... Entangling Shot, Bola, Hungering Arrow, Impale. All awesome skills. Plus more.