Templar & Venatori Archers
You'll find that they're the leading cause of player deaths in this game, mainly do to their sheer numbers and high damage output (especially against Guard and when attacking from the flank). In addition, they have the capacity to generate extremely high amounts of damage after running from a melee player and immediately turning around to fire an arrow (I've seen numbers in the 1000's). That to me should be the biggest fix to them. Aside from that, a very small decrease in damage and fewer numbers of them should even things out.
Templar & Venatori Footsoldiers
These guys can shut down any momentum you might have had if you're a Warrior or Rogue (sometimes even a mage). They're godlike ability to block almost everything is beyond absurd. Here's a short list of things I've seen them block: Whirlwind, Payback Strike, Leaping Shot (12 arrows - WTF!?), Immolate, Hot Licks, Flank Attacks...flank attack, Spirit Blade. Its out of hand - to say the least - and needs a fix (and I'd probably say this should also apply to single player as well if it's as bad as it is in MP).
Templar Shadows and Venatori Stalkers
I'm actually not opposed to them being able to due massive amounts of damage with their flank attack, but Venatori Stalkers need a buff to their flank attack; since it pales in comparison to their Shadow counterpart. Speaking of Shadows, their flank attack is also AoE...so fix that. Either than that, can you also remove them from the first group composition when we have to due the escort objective? There have been times when they outright murder your escort before you can even get to them.
Red Templar Knights and Horrors
Knights should have their amplifying beam range decreased since it can stretch ridiculously far; and sometimes even when there are obstacles in the way. I also think their energy blast could have its velocity reduced some, since its pretty accurate and hard to escape. Horrors should have their back projectiles homing ability toned down some.
Templar and Venatori Mages
Give them higher barriers for themselves, but also fix the spacing between Spellbinder runes so that they don't overlap.
Despair Demons
Could you alter their Ice Mine ability so that it cant be used against you if you're not visible to them? I would also decrease the distance that they can evade when they do their floating.
Pride Demons
The biggest paper tiger in the enemy roster. These guys should be given a lot more guard than they have now, as well as a base health increase. Also, he should be immune to panic abilities. He's the f***ing Pride Demon!
Red Templar Commander
His ability to follow up his leap attack with hard hitting abilities like Earthshattering Strike can be pretty brutal since you're likely still in the middle of recovering if you were knocked down. I think a slight bit of latency in his ability to use different abilities would help give players just a bit more time to recover. I'm not sure what everyone thinks of his Potion I-frames. I find them more annoying than it needing a fix.
Wraiths
Fire Wraiths are the bane of most casual (and even experienced players) due to how much damage they output against you as DoT. I would tack it down since they're can a good number of them and this can ruin any melee players day.