Reasons to re-run end game dungeons: Healing staff v10 set (5% increase to healing done) Achievements (champion points) - Construct set for PVP (20% reduced damage from crits (sneak attacks always crit). Fun. As of 1.5 - Dailies, new undaunted gear - new undocumented sets.

What they need are a whole bunch of dungeon exclusive sets for all classes.

This was put up on Reddit and I'll just repost it here for you.

City of Ash:
Light Armor:
(2pc): 87 Max Magicka
(3pc): 8 Spell Damage
(4pc): 4% Spell Crit
(5pc): 20% chance when dealing Flame damage to inflict the burning status effect on enemy and gain 19 Spell damage for 8s. This effect can occur once every 15s.
Medium Armor:
(2pc): 90 Max Stamina
(3pc): 17 Weapon Damage
(4pc): 4% Weapon Crit
(5pc): When you hit an enemy with a fully charged heavy attack, deal 72 flame Damage and reduce target's armor by 320 for 5s.
Heavy Armor:
(2pc): 135 Max Health
(3pc): 135 Max Health
(4pc): 180 Spell Resistance
(5pc): When you hit an enemy with a fully charged Heavy attack, 50% chance to gain 320 Spell Resistance for 6s. Also deals 96 Flame Damage every second.
Undaunted:
Light Armor:
(2pc): 90 Max Stamina
(3pc): 90 Max Stamina
(4pc): 4% Spell Crit
(5pc): After casting an ability that costs stamina, light attacks deal 72 additional damage and heavy attacks deal 108 additional damage for 10sec
Medium Armor:
(2pc): 90 Max Magicka
(3pc): 90 Max Magicka
(4pc): 4% Weapon Crit
(5pc): After casting an ability that costs Magicka, lights attacks deal 72 additional damage and heavy attacks 108 additional damage for 10s
Tank:
(2pc): 131 Max Health
(3pc): 175 Armor
(4pc): 175 Spell Resistance
(5pc): When you taunt an enemy when below 60% Health, you gain an 1250 Damage shield for 15s, 10s cooldown
2-piece Veteran Dungeon sets
(Head from HM-Boss, Epaulets from Undaunted Chest. Available in Light/Medium/Heavy with random traits):
Banished Cells:
Maw of the Infernal:
(1pc): 129 Max Health
(2pc): 5% chance on light or heavy Attacks to summon a fire breathing deadroth for 15s. Basic attacks deals 188 physical damage.
Fungal Grotto:
Lord Warden Dusk:
(1pc): 180 Spell Resistance
(2pc): 6% chance when hit to summon a shadow orb that adds 480 Spell resistance to nearby allies for 12 seconds
Spindleclutch:
Blood Spawn:
(1pc): 12 Stamina Recovery
(2pc): 6% chance when hit to gain 800 armor and spell Resist for 6s and restore 25 ultimate.
Elden Hollow:
Bogdan the Nightflame:
(1pc): 129 Max Health
(2pc): 2% chance when healing an ally to create a totem for 10 seconds.Totem heals allies in area for 92 every second. This effect has a cooldown of 15 seconds.
Darkshade Caverns:
The Engines Guardian:
(1pc): 11 Health recovery
(2pc): 10% chance on ability use to summon a dwemer automaton to restore 107 Health, Stamina or Magicka every 0.5s for 6.5s.
Wayrest Sewers:
Malubeth the Scourger:
(1pc): 129 Max Health
(2pc): 6% chance when hit to create a beam that steals 720 HP from enemy. Beam breaks from targets greater than 10m away. While beam holds you gain 30% increased healing from all sources.
Crypt of Hearts:
Nerien'eth:
(1pc): 135 Max Health
(2pc): 2% chance when causing damage to create a Lich crystal that explodes after 3s, dealing 520 Magic damage.
City of Ash:
Valkyn Skoria:
(1pc): 135 Max Health
(2pc): 4% chance when damaging an enemy with a damage over time effect to call a meter dealing 720 Flame Damage to target and 360 Flame Damage to other nearby enemies.