PvE is not challenging. It doesn't reward basic strategy, neither it teaches you the basic skill to play pvp. High-End PvE and EoTN, which was meant to be challenging is frustrating instead. Hard Mode is the same.
But the question is: Why?
The reason it is not challenging that it doesn't reward the player's skills. Monsters in hard mode don't reward kiting, because they have a permament IMS. They don't reward interrupts aswell. They only reward bringing mindless and overpowered skills like Save Yourselves and Shadow Form.
Let's see how can it be changed:
Take Blood Rage, the grawl monster skill for example. It increases base damage. Although it may promote prots, it doesnt promote it much more than other monsters. Let's see how can we improve it:
Blood Rage 5 0 15 Stance. For 10 seconds. You attack 25% faster and deal 25% more damage. But you move 33%slower.
It now promotes kiting and stance removal. It's basically flail
Now let's see another example: Enraged.
Enraged 10 0 20 Stance. Attacks and skills do +25% damage but the creature's skills take 50% longer to activate and attacks 25%slower if this creature's Health is below 70%, and an additional +25% damage , skill activation time and the creature attacks 50% slower if its Health is below 30%.
It now rewards interrupts, and is less broken.
Another example: Wurm Bile is one of the most annoying monster skills ever introduced. It is practically a party killer, and when combined with wurm siege, or KD wurms that hit for 50-150 range, or spammed by 3 wurms at once, covered by suffering, it gets really over the top. It is somehow stopped by shadow form. Let's fix it
Wurm Bile 5 3 12 Skill. Deals 40 damage each second (10 seconds). Hits foes nearby to target's initial location. Initial effect: applies Wurm Bile(hex) (8 seconds). End effect: applies a random conditon(12 seconds)
Wurm Bile hex: Causes 50% slowdown and reduces armor by 10.
It's a rather complex effect. It slows enemies down, but can be escaped from. The damage can be avoided, but it still serves as an utility against players. It also goes through both Shadow Form and the "I am Unstoppable!" norn skill. Spreading out and moving can help. Multiple worms don't necessarily decimate the party, but since the effects cumulate, 120 dps is attainable on individual characters, at the cost of being more or less easily avoidable. (3 ticks)
All in all it rewards positioning, an important mechanic in pvp.
Flame shield is pretty much Pain Inverter monster version, and just as it's pve skill counterpart, total bullshit, only rewarding gimmicks without filling any defensive role. Let's change that.
Shield of Fire 10 ¼ 10 Enchantment Spell. For 20 seconds, all damage inflicted to the creature is halved. Half of the taken damage is redirected to the attacker. in short: Creature takes 50% damage, the inflictor takes 25% of that damage back.
Both a shield and a reflective aura. Removable but reapplicable. All in all it's balanced.