My views on these from a melee class standpoint:
Vortex - This one is only bad if it's in combo with a close rang attack like Molten or Arcane. Many a time I have died because I was dodging an Arcane ball and the mob pulled me back into it.
Jailer - More annoying than deadly (depending on the combo).
Molten - This one is one of my least favorites. Makes both kiting and melee hard. Just no good place to stand. I do a lot of jumping in and out with Molten mobs.
Vampiric - One of the easier attributes. He can't suck my blood faster than I can kill him.
Extra Health - Annoying because it makes battles long, but that's about it.
Mortar - Mortar sounds awful but I'm always surprised at how easy these mobs end up being. Get in close and they simply can't hit you. The only time Mortar is a problem is if it's coupled with a close range attribute. Mortar + Fire Chains or Arcane = yikes.
Fire Chains - My second most hated attribute. The mobs are intelligent enough to try to trap you in the chains, so your best bet is to focus on one so that you have fewer chains to dodge.
Arcane - I hate Arcane because it does HUGE damage, but it's easy to dodge. Worst when combined with Vortex (see above).
Plagued - These used to be my most hated, but my resists/HP are high enough now that the poison damage doesn't bother me much. I can typically just stand in a pool of it and whack away.
Waller - More annoying than anything. I just use my Leap ability to jump out of it.
Nightmare - Another one more annoying than dangerous. Most of the time I WANT to run away from the mob so I thank him for helping me.
Couple not mentioned:
Reflect Damage - These reflect damage back when you hit them, but in my experience it's not enough to make much of a difference.
Frozen - Another annoying one. Mob casts several ice spheres that explode and freeze you if you are within range. They can be dodged but a lot of times I'll just suck it up and take the hits just so I can stay close to attack range.