It's really two main concerns.
1. Mana. I have now brought a second class up through nightmare, a wizard, and he never has resource issues and is doing much better overall. My WD, on the other hand, is constantly out of mana. From reading the forums, it's not just me either. Using one of dire bats/acid cloud/locust swarm/zombie charger/etc plus a GotD expels my mana so fast it has caused many a death for me. And this is without PtV.
2. Pets. I tried to convince myself (and other people at times) in beta that pets would be fine, they'd scale, they weren't meant to tank bosses all day, etc etc. But let's just call a spade a spade: our pets suck. Gargantuan is somewhat decent through normal and can actually survive some of the boss encounters. Not in NM and beyond. And Zombie dogs, holy cow, they don't stay up for more than 1 swarm of regular monsters in Act 4 of normal, let alone anywhere else or bosses/champions.. and this is while built with passives to buff them! What a waste. If you use Hedge Magic it helps them in norm, but even then in NM they die so fast there is nothing you can do. Sacrifice is a nice way to get damage out of them, but the 60 second cooldown makes this not practical in NM/Hell for me. IMO they were meant to be passive dps/distractions that don't need to be recast every 2 seconds, and they clearly are not fulfilling that role.
-Doesn't it seem like some of the WD's skills are useless? Does anybody use toad of hugeness as something more than "that looks cool"? There might be some situations where it helps but Hex is better in 99.9% of all scenarios. Maybe make it so you use your regular plague of toads attack, and with that rune the Huge toad comes out in addition.
-Spider Queen, really?
-Is MC truly worthy of a 60 second cooldown? The wizard gets basically a 6 second 100% damage mitigation every 15 seconds (diamond skin), and we have to wait 60 seconds for unreliable CC that doesn't effect most of the enemies in an area? Ok this was a bit of a QQ :)
-The best skill damage and range to mana by far (even though it still drains your mana) is Dire Bats, which you get at level 11. Kinda negates all those cool looking skills you get later.
So with that in mind, I think if Blizz could do just one of the following I'd be willing to throw a parade for them:
-Lower the mana cost for all or most of the secondary/decay abilities.
-Increase pet damage/survivability
-Decrease the cooldown on our perma pets and/or some of our CC like MC/Wall of Zombies.
I believe that the way the WD is now, is intentional because Blizz was nervous that if they made it as easy as for the WD to have the same DPS as, say a Wiz or DH, it would be OP because they have perma pets (a valid concern). But I think they went overboard in the sense that in NM and beyond the pets are essentially useless, and in order to have dps on par with other classes you've got to jump through hoops (soul harvest/ptv) and sacrifice either all mana efficiency or all survivability.
TL;DR: WD has serious mana issues, our pets suck, and many useful abilities have a prohibitively long cooldown. These issues can easily be addressed in my opinion.
Thoughts? Hate mail? What do you guys think? Maybe I just need to "L2P" but I have done fine through the same content on a different class.