Dropping mage duels, harsh counters and overpowered items in PoE is not sticking to the original formula.
Eh, there's plenty of seriously overpowered items in PoE. Not many hard counters perhaps, but having items that boost defense vs an ailment by +30 is pretty damn good and should generally be enough.
Mage duels are indeed notably absent.
Nothing like Gram the sword of grief, which drains one level per hit Or Aslyferund Elven Chain which makes you completely immune to unenchanted weapons is in BG2 is in PoE.
Gram: Pretty neat, though the enemies still have to fail the death save. Wonder how often that happens at the Throne of Bhaal levels when you get the level draining effect.
Aslyferund Elven Chain: Immune to mundane. Really? Too bad almost noone uses unenchanted weapons when you get it. Still a good armor for a mage or bard.
Meanwhile in PoE we have among others:
Stormcaller: A fast hunting bow which has a 10% chance to cast Returning Storm on hit when wielded by a Ranger, which does good damage and stuns enemies in a large radius AND attacks with this bow lower enemy resistance to Shock AND it deals Pierce/Shock damage, whichever the enemies resist less. This item is considered unfair by many and some shun using it in their games, since it stunlocks entire crowds indefinitely, while dealing high damage.
Cipher and Chanter also get strong Shock spells from their respective spellbooks on hit.
Steadfast: a sword that grants Outmanouvering passive to Fighters, Chanters and Wizards. Making them target enemy Willpower rather then Deflection (AC), if it's lower. It also gives immunity to Fear.
For other classes it may cast Sunlance on Hit, Champion's Boon (+10 Might, +10 Per & +5DR) on kill or Restore Major Endurance.
Shod-In-Faith: Boots that cast Consecrated Ground when Critically Hit: a powerful aoe heal-over-time, which mostly eliminates the need for individual healing spells.
Armor, Cloak, Shield which grant Retaliate (which stack).
The Unlabored Blade: a dagger with a small chance to cast a powerfull offensive bouncing spell Firebug on Crit. Crits happen very often though, especially for a barbarian who attacks in a huge aoe. Also +20% attack speed, some other spells per rest, up to Mythic quality.
Ryona's Breastplate: Various powerful defensive buffs
St. Ydwen's Redeemer: already mentioned, kills Vessels (undead) on hit. May also cast Pillar of Faith for a Fighter (damage+knockdown), Divine Mark for a Paladin (damage + AC debuff) or Despondent Blows (ToHit debuff) for Barbarians. Plus Revive 1/rest.
Abydon's Hammer: kills Eyeless on crit and many other powers.
Forgemaster's Gloves: Summons Firebrand 3x per rest. Firebrand is a flaming sword which deals purely Fire damage, has much higher base damage and +0,5 Crit damage modifier. Makes a Barbarian's aoe Carnage explode with each attack, like a human fireball. Is buffed by Scion of Flame. Note it was nerfed, because at launch the sword targeted enemy Reflex defence, rather then Deflection (AC), so was completly overpowered vs most enemies.
Many "regular" artifacts Prone on Crit, Stun on Crit and do other nasty stuff. Note Crits are much easier to achiever in PoE then in IE games. You can buff accuracy in relation to enemy (lowered) deflection by roughly 60 pts. And you have effects with 20-30% Hit to Crit conversion.
So I could list many other items that are VERY strong. But I think that's enough for now.